Amicus Curiae Brief — William Trevor Case, Petitioner v. Montana

Supreme Court briefAug 6, 2025

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No. 24-624

IN THE

Supreme Court of the United States

WILLIAM TREVOR CASE,

Petitioner,

STATE OF MONTANA,

Respondent.

On Writ of Certiorari to the

Montana Supreme Court

BRIEF OF CONSTITUTIONAL ACCOUNTABILITY

CENTER AS AMICUS CURIAE IN

SUPPORT OF PETITIONER

ELIZABETH B. WYDRA

BRIANNE J. GOROD*

BRIAN R. FRAZELLE

MIRIAM BECKER-COHEN

CONSTITUTIONAL

ACCOUNTABILITY CENTER

1730 Rhode Island Ave. NW

Suite 1200

Washington, D.C. 20036

(202) 296-6889

brianne@theusconstitution.org

Counsel for Amicus Curiae

August 6, 2025

* Counsel of Record

TABLE OF CONTENTS

Page

TABLE OF AUTHORITIES .................................

INTEREST OF AMICUS CURIAE ......................

INTRODUCTION AND SUMMARY OF

ARGUMENT ......................................................

ARGUMENT .........................................................

Founding-Era Common Law Required

More Than Probable Cause, Not Less,

for Warrantless Home Entries ..............

The Fourth Amendment’s Chief Aim

Was to Restrain Discretionary

Searches of the Home .............................

III. The Framers Viewed Probable Cause

as a Vital Safeguard Against

Unfounded Searches and Seizures .......

CONCLUSION .....................................................

II.

(i)

TABLE OF AUTHORITIES

Page(s)

Cases

Atwater v. Lago Vista,

532 U.S. 318 (2001) .....................................

8, 14

Bostock v Saunders,

95 Eng. Rep. 1141 (K.B. 1773) ....................

Bostock v Saunders,

96 Eng. Rep. 539 (K.B. 1773) ......................

5, 24

Boyd v. United States,

116 U.S. 616 (1886) .....................................

California v. Ciraolo,

476 U.S. 207 (1986) .....................................

Entick v. Carrington,

19 How. St. Tr. 1029 (C.P. 1765) ................ 18, 25

Florida v. Jardines,

569 U.S. 1 (2013) .........................................

Lange v. California,

594 U.S. 295 (2021) ................................ 6-8, 10-13

Leach v. Money,

19 How. St. Tr. 1001 (K.B. 1765) ................ 24, 25

R. v. de Wellingborough (K.B. 1326), in

4 Select Cases in the Court of King’s Bench

Under Edward II (G.O. Sayles ed., 1957)...

Regina v. Tooley,

92 Eng. Rep. 349 (Q.B. 1710) ......................

iii

TABLE OF AUTHORITIES – cont’d

Page(s)

Riley v. California,

573 U.S. 373 (2014) .....................................

Semayne’s Case,

77 Eng. Rep. 194 (K.B. 1604) ......................

Sir Anthony Ashley’s Case,

77 Eng. Rep. 1366 (St. Ch.1611) .................

State v. Freeman,

86 N.C. 683 (1882) .......................................

Tennessee v. Garner,

471 U.S. 1 (1985) .........................................

Ughtred v. Musgrave (King’s Council, 1366),

in Select Cases Before the King’s Council,

1243–1482 (I.S. Leadam ed.,1918) ..............

United States v. Jones,

565 U.S. 400 (2012) .....................................

United States v. U.S. Dist. Court for E. Dist.

of Mich.,

407 U.S. 297 (1972) .....................................

Virginia v. Moore,

553 U.S. 164 (2008) .....................................

Wilkes v. Wood,

19 How. St. Tr. 1153 (C.P. 1763) ................

Wilson v. Layne,

526 U.S. 603 (1999) .....................................

TABLE OF AUTHORITIES – cont’d

Page(s)

Wyoming v. Houghton,

526 U.S. 295 (1999) .....................................

6, 15

Statutes, Constitutional Provisions, and Legislative

Materials

Act of Frauds of 1662, 12 Car. 2, reprinted

in 8 The Statutes at Large of England and

Great-Britain (1763) ....................................

Act of July 31, 1789, ch. 5, 1 Stat. 29 ............ 26, 27

Act of Mar. 3, 1791, ch. 15, 1 Stat. 199 .........

Annals of Cong. (1789) (Joseph Gales ed.,

1834).............................................................

Mass. Const. art. XIV (1780) .........................

Pa. Const. of 1776, Decl. of Rights, art. X .....

U.S. Const. amend. IV ...................................

4, 15

Va. Decl. of Rights (1776) ..............................

Books, Articles, and Other Authorities

Thomas Barrow, Trade and Empire: The

British Customs Service in Colonial

America, 1660–1775 (1967) .........................

3 William Blackstone, Commentaries on the

Laws of England (1766) ..............................

4 William Blackstone, Commentaries on the

Laws of England (1791) .............. 2, 7-9, 11, 12, 24

TABLE OF AUTHORITIES – cont’d

Page(s)

Henry de Bracton, Bracton on the Laws

and Customs of England (George

Woodbine ed., 1968)................................... 4, 21, 22

Richard Burn, The Justice of the Peace,

and Parish Officer (1758) ...................... 9-12, 14, 24

Joseph Chitty, Practical Treatise on the

Criminal Law (Edward Earle ed.,

1819).................................................... 8, 10, 12, 24

2 Edward Coke, Institutes of the Laws

of England (1681) ........................................

4 Edward Coke, Institutes of the Laws of

England (1797) ............................................ 11, 12

A Columbian Patriot, Observations on the

New Constitution, and on the Federal and

State Conventions, reprinted in Pamphlets

on the Constitution of the United States

(Paul Leicester Ford ed., 1888). ..................

William J. Cuddihy, The Fourth Amendment:

Origins and Original Meaning

(2009) ....................................... 5, 18, 19-21, 23-26

Michael Dalton, The Country Justice

(1690) ...........................................................

9, 22

Thomas Y. Davies, Recovering the Original

Fourth Amendment, 98 Mich. L. Rev. 547

(1999) .................................................. 7, 15, 16, 18

TABLE OF AUTHORITIES – cont’d

Page(s)

The Debates in the Several State Conventions

on the Adoption of the Federal Constitution

(Jonathan Elliot ed., 1836) ..........................

Laura K. Donahue, The Original Fourth

Amendment, 83 U. Chi. L. Rev. 1181

(2016) ...........................................................

Edward Hyde East, Treatise of the Pleas of

the Crown (1803). ........................................ 12, 13

Essay by a Farmer and Planter, Md. Journal,

Mar. 27, 1788, in 5 The Complete AntiFederalist (Herbert J. Storing ed., 1981) ....

Lawrence M. Friedman, Crime and

Punishment in American History (1993) ....

Matthew Hale, History of the Pleas of

the Crown (1736) ............................. 7, 8, 10-13, 23

1 William Hawkins, A Treatise of the Pleas

of the Crown (1777) .....................................

2, 11

2 William Hawkins, A Treatise of the Pleas

of the Crown (1787) ......................... 5, 8, 10-14, 23

Giles Jacob, A New Law Dictionary (1739) ... 13, 14

Tracey Maclin, The Complexity of the

Fourth Amendment: A Historical Review,

77 B.U. L. Rev. 925 (1997) .......................... 20, 25

vii

TABLE OF AUTHORITIES – cont’d

Page(s)

Hon. M. Blane Michael, Reading the Fourth

Amendment: Guidance from the Mischief

That Gave It Birth, 85 N.Y.U. L. Rev. 905

(2010) ........................................................... 16, 17

James Parker, The Conductor Generalis (Pa.

1792).............................................................

Frederick Pollock & Frederic William

Maitland, The History of English Law Before

the Time of Edward I (2d ed. 1898) ............

Barbara J. Shapiro, Beyond Reasonable

Doubt and Probable Cause: Historical

Perspectives on the Anglo-American Law

of Evidence (1991) ...................................... 5, 22, 24

William Sheppard, An Epitome of All the

Common and Statute Laws of the Nation

(1656) ...........................................................

5, 23

William Sheppard, The Offices of Constables

(1657) ........................................................... 10, 11

Carol S. Steiker, Second Thoughts About

First Principles, 107 Harv. L. Rev. 820

(1994) ...........................................................

James Fitzjames Stephen, History of the

Criminal Law of England (1883) ................

8, 10

Joseph Story, Commentaries on the

Constitution of the United States (1833).....

viii

TABLE OF AUTHORITIES – cont’d

Page(s)

Andrew E. Taslitz, Reconstructing the

Fourth Amendment: A History of Search

and Seizure, 1789–1868 (2006) .......... 20-22, 24, 25

George Webb, The Office and Authority of

a Justice of Peace (Va. 1736) ................... 10, 11, 14

Jack K. Weber, The Birth of Probable Cause,

11 Anglo-Am. L. Rev. 155 (1982) ................

Saunders Welch, Essay on the Office of

Constable, reprinted in James Parker,

Conductor Generalis (N.J. 1764)............... 9, 12, 14

Horace L. Wilgus, Arrest Without a Warrant,

22 Mich. L. Rev. 541 (1924).........................

Works of John Adams (Charles Francis

Adams ed., 1850) ......................................... 17, 25

INTEREST OF AMICUS CURIAE1

Constitutional Accountability Center (CAC) is a

think tank and public interest law firm dedicated to

fulfilling the progressive promise of the Constitution’s

text and history. CAC has a strong interest in ensuring that the Constitution applies as robustly as its text

and history require and accordingly has an interest in

this case.

INTRODUCTION AND

SUMMARY OF ARGUMENT

Police officers must sometimes consider whether

to enter a home without permission based on reports

that someone inside may need emergency aid. But police officers are not like neighbors offering assistance:

they carry deadly weapons, are charged with acting

upon potential lawbreaking they observe, and may

use lethal force when they perceive threats to their

safety during split-second encounters. Forcibly entering homes when there is no emergency can thus put

lives in jeopardy. And if mere suspicion that someone

might be in danger were enough to allow warrantless

police entries, the sanctity of the home would be placed

at risk of groundless and even pretextual government

intrusions. This Court’s precedents therefore require

that such entries be supported by probable cause. The

Fourth Amendment’s text and history compel the

same result.

1. Under Founding-era common law, which provides a baseline for reasonableness under the Fourth

1 No counsel for a party authored this brief in whole or in part,

and no counsel or party made a monetary contribution intended

to fund its preparation or submission. No person other than amicus or its counsel made a monetary contribution to its preparation

or submission.

Amendment, much more than probable cause was

needed for officers to forcibly enter homes, for any purpose.

The common law did not allow law enforcement officers to break into homes to provide emergency aid.

The only similar power officers wielded was to enter

homes without warrants to stop violent “affrays.” But

such entry required more than probable cause, not

less. Indeed, it required certainty. Officers could not

respond to an affray, even in public, without personally observing it with their own senses. If an affray

occurred out of an officer’s view, he had no power to

intervene or arrest the participants. It was well

known, therefore, that officers had to personally witness an affray before they could take the extreme

measure of forcibly entering a home to stop the affray

or apprehend the offenders.

Indeed, many authorities limited the very definition of an affray to publicly visible disturbances. An

affray was typically understood as “the fighting of two

or more persons in some public place, to the terror of

his majesty’s subjects,” and so “if the fighting be in private, it is no affray.” 4 William Blackstone, Commentaries on the Laws of England 145 (1791). Unless observers could perceive the tumult inside a home, “it

cannot be said to be to the terror of the people.” 1 William Hawkins, A Treatise of the Pleas of the Crown 265

(1777). And without that, law enforcement officers

had no right to intervene, much less force their way

into homes to do so.

The common law was just as strict about the other

conditions that allowed warrantless home entries—

there, too, more than probable cause was required.

One set of rules governed arrests for felonies, a category limited to a small handful of the most serious

crimes. Officers could forcibly enter a home in pursuit

of a fleeing felon, or a perpetrator whose violence had

put someone at risk of dying (an event that would

make the perpetrator a felon). Likewise, officers could

break into homes to arrest such offenders when taking

part in the “hue and cry,” the age-old method of gathering townspeople to capture felons. But warrantless

entry for felony arrests required significantly more

than probable cause. This extreme measure was available only if it was certain that a felony or a dangerous

wounding had actually occurred, and only if the officer

had probable cause to believe that the suspect was the

culprit. Moreover, if an officer turned out to be wrong

that a house contained the suspect in question, the officer was liable for trespass. In short, certainty was

required about the existence of a crime and the location of the suspect, along with probable cause of the

suspect’s guilt.

Officers also could forcibly enter homes to recapture arrestees who had escaped, an offense that itself

was originally a felony. But probable cause alone did

not suffice here either. Certainty was required, because nothing shielded officers from liability if they

were wrong that a home harbored an escapee.

All told, the common law never allowed law enforcement officers who lacked a warrant to enter

homes with anything less than probable cause. On the

contrary, the common law demanded much more.

2. The Constitution’s Framers were no less concerned about defending the sanctity of the home. The

Fourth Amendment was meant to preserve common

law protections against unbridled search and seizure,

inspired by the colonists’ experience with general warrants that lacked individualized suspicion backed by

credible evidence. As early as the 1600s, the use of

such warrants came under attack in England. They

were decried as instruments of arbitrary power, and

popular opposition to them quickly solidified as they

were used to ransack the homes of vocal critics of the

government. During the 1700s, colonists also began to

speak out against general warrants, and their use was

one of the chief grievances that inspired the movement

for independence from British rule.

Fears of home intrusion under general warrants

continued in the post-colonial period, as state leaders

called for the nation’s federal charter to include an

explicit protection against such arbitrary power. The

Fourth Amendment’s text reflects the Framers’

staunch opposition to the use of general warrants to

invade the home, expressly shielding “houses” from

unreasonable searches and requiring all warrants to

be predicated on “probable cause, supported by Oath

or affirmation.” U.S. Const. amend. IV. This text reflects the Framers’ core concern with preventing government searches in the absence of some adequate reason to believe the search is necessary. Fundamentally,

the Framers wrote the Fourth Amendment to strip law

enforcement officers of the power to intrude upon a

person’s most private spaces without a strong basis for

doing so.

3. While the Fourth Amendment mentions probable cause only in its Warrant Clause, the Framers understood that standard to be a more general safeguard

against unreasonable searches and seizures.

The concept of probable cause developed independently from the use of warrants. In medieval

times, English common law courts were already evaluating whether warrantless arrests were supported by

adequate cause. This was deemed essential because

“uproar and public outcry are at times made of many

things which in truth have no foundation.” 2 Bracton

on the Laws and Customs of England 404 (George

Woodbine ed., 1968).

By the fifteenth century, it was clear that “good

evidence” was required to arrest suspected criminals

without warrants. Barbara J. Shapiro, Beyond Reasonable Doubt and Probable Cause: Historical Perspectives on the Anglo-American Law of Evidence 129

(1991). Probable cause came into even sharper focus

with the proliferation of justice-of-the-peace manuals

in the sixteenth century. These manuals described

various acceptable causes of suspicion for arrest, while

warning that “whether the cause of suspicion be good”

could be tested in a false imprisonment action. William Sheppard, An Epitome of All the Common and

Statute Laws of the Nation 650 (1656).

At the Founding, probable cause had become even

more clearly identified as an evidentiary threshold distinct from mere suspicion. Someone making a warrantless arrest would have to show the “cause which

induced him to have such a suspicion,” which must

“appear to the court to have been a sufficient ground.”

2 Hawkins, A Treatise of the Pleas of the Crown 121

(1787). Warrants could not be granted “without such

a probable cause, as might induce a candid and impartial man to suspect the party to be guilty.” Id. at 136.

And the leading precedent on probable cause, which

held an officer liable for a fruitless search, explained

that “the suspicion must be very well founded to justify

entering a house without the owner’s consent.” Bostock v Saunders, 96 Eng. Rep. 539, 540 (K.B. 1773)

(de Grey).

Conflict between Britain and the colonies helped

further enhance the focus on probable cause. Apart

from the general-warrant controversies discussed

above, the warrantless seizure of American ships for

alleged customs violations incited widespread protests

condemning the lack of “any probable cause of seizure

that we know of.” William J. Cuddihy, The Fourth

Amendment: Origins and Original Meaning 589 (2009)

(quoting comments of Boston town meeting). After Independence, states enacted protections against

searches and seizures unsupported by adequate cause,

which were later echoed in the Fourth Amendment.

And as that Amendment was being drafted, the First

Congress passed measures reflecting the view that

probable cause was an important constraint on

searches and seizures, including in situations where

no warrant was required.

Thus, from the Middle Ages to the Fourth Amendment’s adoption, the requirement of probable cause

served as a valuable safeguard against unfounded

searches and seizures. It remains so today, even when

the professed reason for which police officers break

into homes is to provide emergency aid.

ARGUMENT

Founding-Era Common Law Required More

Than Probable Cause, Not Less, for

Warrantless Home Entries.

“The common law in place at the Constitution’s

founding” provides “a baseline” for reasonableness under the Fourth Amendment. Lange v. California, 594

U.S. 295, 309 (2021). The Amendment “was meant to

preserve” certain common law “norms,” Virginia v.

Moore, 553 U.S. 164, 168 (2008), and it “must provide

at a minimum the degree of protection it afforded

when it was adopted,” Lange, 594 U.S. at 309 (quoting

United States v. Jones, 565 U.S. 400, 411 (2012) (emphasis in original)).

On the question presented in this case, the inquiry

into common law norms yields a clear answer. See Wyoming v. Houghton, 526 U.S. 295, 299 (1999). Law enforcement officers may not enter a home with less than

probable cause to believe that an exigency exists.

Professional police officers were “unknown to the

common law.” State v. Freeman, 86 N.C. 683, 684

(1882). “There were no police in the modern sense”

during the Founding era, and “justice was a business

of amateurs.” Lawrence M. Friedman, Crime and

Punishment in American History 27-28 (1993). “Public

order was maintained by a loose system of sheriffs,

constables, and night watchmen,” with the constable

carrying “the main burden of law enforcement.” Carol

S. Steiker, Second Thoughts About First Principles,

107 Harv. L. Rev. 820, 830 (1994). Constables were

usually low-status individuals “pressed into a tour of

duty for a year.” Thomas Y. Davies, Recovering the

Original Fourth Amendment, 98 Mich. L. Rev. 547, 620

(1999).

The common law did not allow law enforcement officers to forcibly enter homes—referred to as “breaking

doors”—to render emergency aid.2 Indeed, with only

limited exceptions, public officers and private individuals alike were forbidden from entering homes for any

purpose without a warrant, “[f]or every man’s house

[was] looked upon by the law to be his castle of defense

and asylum,” and “not so much as a common citation

or summons . . . [could] be executed upon a man within

his own walls.” 3 William Blackstone, Commentaries

on the Laws of England 288 (1766). As a general rule,

therefore, warrants were essential “before a government official could enter a house.” Lange, 594 U.S. at

310. And while that rule had narrow exceptions, “in

all cases where the law [was] silent, and express

2 The term “breaking doors” meant removing any barrier to entry, such as “lifting up the latch of a door, or unloosing any other

fastening which the owner has provided.” 4 Blackstone, supra, at

226; see 1 Matthew Hale, History of the Pleas of the Crown 55152 (1736) (“every one, that enters into another’s house against his

will . . . doth in law break the house”).

principles [did] not apply, this extreme violence [was]

illegal.” 1 Joseph Chitty, Practical Treatise on the

Criminal Law 35 (Edward Earle ed., 1819).3

Rendering aid was not among the exceptions to the

warrant requirement. Instead, officers could forcibly

enter homes for only three reasons: to stop an affray

(or arrest the offender), to make a felony arrest, and to

recapture an escaped arrestee. All three scenarios required much more than probable cause.

Most relevant here, officers could forcibly enter

homes to stop violent “affrays” and “breaches of the

peace,” or to arrest the participants. “[A] typical example was ‘the fighting of two or more persons’ to ‘the

terror of his majesty’s subjects.’” Lange, 594 U.S. at

312 (quoting 4 Blackstone, supra, at 145). This authority was the only power sanctioned by common law

that resembled this Court’s emergency-aid doctrine. If

there were “likely to be manslaughter or bloodshed

committed” during “an affray in a house, where the

doors are shut,” the constable could “break open the

doors to keep the peace and prevent the danger.”

2 Matthew Hale, History of the Pleas of the Crown 95

(1736); accord 2 William Hawkins, A Treatise of the

Pleas of the Crown 139 (1787); see 4 Blackstone, supra,

at 145 (permitting breaking doors “to suppress an affray, or apprehend the affrayers”).4

3 Spelling and capitalization from historical sources have been

changed to modern usage throughout this brief.

4 The term “breach of the peace” generally signified “an element

of violence” when used “in reference to common-law arrest

power.” Atwater v. Lago Vista, 532 U.S. 318, 327-28 n.2 (2001);

accord 1 James Fitzjames Stephen, History of the Criminal Law

of England 193 (1883).

The standard required for these entries was higher

than probable cause—it was certainty, confirmed by

an officer’s own senses. Officers had to personally witness an affray before they could intervene, even in

public. “The constable . . . [could] without warrant, arrest any one for a breach of the peace committed in his

view,” 4 Blackstone, supra, at 292 (emphasis added),

but he had “no power to arrest a man for an affray done

out of his own view, without a warrant,” Richard Burn,

The Justice of the Peace, and Parish Officer 9 (1758);

2 Edward Coke, Institutes of the Laws of England 52

(1681) (“after the affray [is] ended, they cannot be arrested without an express Warrant”); James Parker,

The Conductor Generalis 12 (Pa. 1792) (“a constable is

. . . empowered . . . to part an affray which happens in

his presence” and to arrest participants “if a constable

see persons . . . actually engaged in an affray” (emphasis added)).

Even in public, therefore, officers could arrest only

when an affray was “committed in [their] presence and

followed by immediate and continuous pursuit.” Horace L. Wilgus, Arrest Without a Warrant, 22 Mich. L.

Rev. 541, 701 (1924); see Regina v. Tooley, 92 Eng. Rep.

349, 352 (Q.B. 1710) (“a constable cannot arrest, but

when he sees an actual breach of the peace; and if the

affray be over, he cannot arrest”); Michael Dalton, The

Country Justice 36 (1690) (“After the affray . . . the

constable, without a warrant, cannot arrest the affrayors.”); Saunders Welch, Essay on the Office of Constable, reprinted in James Parker, Conductor Generalis 111, 115 (N.J. 1764) (“after the affray or assault

is over . . . the injured person ought to apply to a magistrate for his warrant”). Simply put, the power to respond to an affray or breach of the peace was “limited

to cases in which the person to be arrested was taken

in the fact or immediately after its commission.” 1 Stephen, supra, at 193.5

Given these strict limits on interfering with affrays even in public, warrantless home entry for that

purpose likewise demanded that officers rely only on

their own direct knowledge of the affray. Officers

could not forcibly enter based on probable cause or the

reports of others. Entry was permitted only when an

“affray is made in a house in the view or hearing of a

constable; or where those who have made an affray in

his presence fly to a house, and are immediately pursued by him.” 2 Hawkins, supra, at 139 (emphasis

added); accord 1 Chitty, supra, at 35 (“when an affray

is made in a house, in the view or hearing of a constable, he may break open the outer door in order to suppress it” (emphasis added)); Burn, supra, at 9 (“if an

affray be in a house, the constable may break open the

doors to preserve the peace; and if affrayers fly to a

house, and he follow with fresh [pur]suit, he may break

open the doors to take them” (emphasis added));

George Webb, The Office and Authority of a Justice of

Peace 6 (Va. 1736) (“if the affray be in his view,” a constable “may break open an house to take the offenders”); William Sheppard, The Offices of Constables 8-9

(1657) (“If he that doth make the affray, when he doth

see the officer coming to arrest him, shall fly into a

house, the officer may in the fresh pursuit of him,

break open the doors upon him to take him.” (emphasis

added)).

5 Only Matthew Hale seems to have suggested that officers

could arrest for affrays committed outside their view. See 2 Hale,

supra, at 90; but see 1 id. at 587 (acknowledging that the contrary

“hath been held”). And Hale did not clearly indicate whether he

endorsed forcible entry to respond to an affray without an officer’s

personal observation of it. See 2 id. at 95; cf. Lange, 594 U.S. at

312 (describing another issue on which Hale was an outlier).

Indeed, many commentators limited the very definition of an affray to publicly visible disturbances, consistent with the rule that officers must personally witness an affray before intervening. Cf. Lange, 594 U.S.

at 335 (Roberts, J., concurring in the judgment) (defining “affray” as “public fighting”). Blackstone, for instance, defined affray as “the fighting of two or more

persons in some public place, to the terror of his majesty’s subjects; for, if the fighting be in private, it is no

affray but an assault.” 4 Blackstone, supra, at 145

(emphasis added); see id. (noting the word’s etymological roots in “affraier, to terrify”); accord 1 Hawkins,

supra, at 265 (defining “affray” as “a public offense, to

the terror of the people,” while excluding an assault

that “happens in a private place . . . in which case it

cannot be said to be to the terror of the people”).

In short, breaking doors to respond to affrays—the

only common law authority resembling emergency

aid—required personal knowledge of the exigency, not

merely probable cause, and certainly not anything

less.

The two other reasons for which officers could

make warrantless home entries were similarly restricted—each required more than probable cause.

One set of rules governed felony arrests. If a fleeing

felon took refuge in a home, officers could “break open

doors to take the felon.” 2 Hale, supra, at 90; accord

4 Edward Coke, Institutes of the Laws of England 17677 (1797); 2 Hawkins, supra, at 139; 4 Blackstone, supra, at 293; Sheppard, Offices, supra, at 15; Webb, supra, at 145. This rule “extended to crimes that would

become felonies if the victims died,” Lange, 594 U.S. at

312, i.e., to “a dangerous wounding,” 4 Blackstone, supra, at 292; accord 4 Coke, supra, at 177; 2 Hale, supra, at 94; 2 Hawkins, supra, at 139; Burn, supra, at

46. In addition, “[m]ost of the common-law authorities

approved warrantless home entries upon a hue and

cry,” Lange, 594 U.S. at 312 n.6, which was “the old

common law process of pursuing, with horn and with

voice, all felons, and such as have dangerously

wounded another,” 4 Blackstone, supra, at 293; accord

4 Coke, supra, at 177; 2 Hale, supra, at 94; Burn, supra, at 392.

Warrantless entry for a felony arrest required significantly more than probable cause: entry was permitted only if a felony or dangerous wounding had actually occurred, and only if there were probable cause

to believe the suspect was the culprit. See 4 Blackstone, supra, at 292 (for a “felony actually committed,”

officers could forcibly enter to arrest those suspected

with “probable suspicion” (emphasis in original));

2 Hale, supra, at 92 (“there must be a felony in fact

done,” and “just grounds of suspicion” that the arrestee

committed it); 1 Hale, supra, at 588 (“probable cause

of suspicion”); Parker, supra, at 117 (requiring “first,

that a felony has been really committed; and, secondly,

that the person you arrest is properly suspected”). In

short, warrantless entry was allowed when it was “certain that a . . . felony [had] been committed, or a dangerous wound given,” 1 Chitty, supra, at 35, and even

then, when a felony was “actually committed,” a “bare

suspicion of guilt against the party [would] not warrant a proceeding to this extremity,” 1 Edward Hyde

East, Treatise of the Pleas of the Crown 322 (1803).

Some authorities were even stricter, disallowing

forcible entry for felony arrests with a warrant, and

instead demanding an indictment. “[W]here one lies

under a probable suspicion only, and is not indicted,”

William Hawkins wrote, “it seems the better opinion

at this day, [t]hat no one can justify the breaking open

doors in order to apprehend him.” 2 Hawkins, supra,

at 139 (footnote omitted); accord Burn, supra, at 46;

4 Coke, supra, at 177 (“for justices of peace to make

warrants upon surmises, for breaking the houses of

any subjects to search for felons . . . is against Magna

Carta”).

Additionally, officers were subject to liability if

they forcibly entered a home to arrest a suspect who

was not there. See 1 East, supra, at 324 (“where the

doors . . . are broken open upon supposition of the person sought being there, it must be at the peril of finding him there: unless as it seems where the parties act

under a magistrate’s warrant”).

Probable cause

shielded only mistaken beliefs about a suspect’s guilt,

not about his location. See, e.g., 1 Hale, supra, at 58889. So if a suspect turned out to be absent from a home

the officer entered without a warrant, that officer

would be liable for trespass.

Significantly, too, “[t]he felony category then was

a good deal narrower than now,” Lange, 594 U.S. at

311, encompassing only a small handful of the most

serious crimes, see “Felony,” Giles Jacob, A New Law

Dictionary (1739). Indeed, “virtually all felonies were

punishable by death.” Tennessee v. Garner, 471 U.S.

1, 13 (1985).

In sum, the felony-arrest exception allowed warrantless entry for only the gravest of crimes. It required certainty that a qualifying crime was committed. It required certainty that the person being sought

was in the house. And even then, it required at least

probable cause that the suspect was guilty.

Finally, officers could forcibly enter homes to recapture escaped arrestees. See 2 Hawkins, supra, at

139 (allowing entry “[w]herever a person is lawfully

arrested for any cause and afterward escapes, and

shelters him in a house” (footnote omitted)); Lange,

594 U.S. at 311 n.5. This rule also arose from the need

to arrest felons: escaping from an arrest, often called

“prison breaking,” was originally a felony under common law, even when the underlying crime was only a

misdemeanor. See 2 Hawkins, supra, at 190, 194-95;

Burn, supra, at 609-10. A statute modified that rule,

see id., but some authorities in the eighteenth century

still maintained “[t]hat such an escape amounts to felony,” 2 Hawkins, supra, at 189; see, e.g., Jacob, A New

Law Dictionary, supra (defining “felony” as including

breach of prison); Webb, supra, at 145 (categorizing

escape as a felony).

Regardless, the standards governing warrantless

entry to recapture an arrestee were just as strict as

those governing an initial arrest: probable cause alone

did not suffice. No special rule shielded officers who

turned out to be wrong that a home harbored an escapee. See, e.g., 2 Hawkins, supra, at 138-39. Instead,

officers who made that mistake were liable for trespass, despite having reasonably believed an escapee

was present, because their intrusion did not fall within

any of the recognized justifications for warrantless

entry. See id.; cf. Parker, supra, at 117 (explaining

that an error about whether an arrestee was “properly

suspected” of felony was “excusable in the law”).

To sum up, the only common law authority resembling the emergency-aid doctrine required personal

knowledge of an exigency, directly confirmed by an officer’s own senses. That rule was in harmony with the

common law’s militant protection of the home from unnecessary intrusion, which consistently required more

than probable cause, not less. On the question presented in this case, the common law spoke with “unanimity.” Atwater v. City of Lago Vista, 532 U.S. 318,

332 (2001). Officers could not forcibly enter homes

based on probable cause that an exigency might exist,

let alone based on some lesser degree of suspicion.

II. The Fourth Amendment’s Chief Aim Was to

Restrain Discretionary Searches of the

Home.

The Constitution’s Framers were just as concerned

as the English common law with preserving the sanctity of the home. As text and history confirm, “physical

entry of the home is the chief evil against which the

wording of the Fourth Amendment is directed.”

United States v. U.S. Dist. Court for E. Dist. of Mich.,

407 U.S. 297, 313 (1972). Thus, “when it comes to the

Fourth Amendment, the home is first among equals,”

Florida v. Jardines, 569 U.S. 1, 6 (2013), and it is the

place where privacy interests are “most heightened,”

California v. Ciraolo, 476 U.S. 207, 213 (1986).

As described above, the concept of the home as a

place of enhanced personal security was a pervasive

theme in English common law, a sentiment reflected

in the oft-cited statement that “the house of every one

is to him as his castle and fortress, as well for his defense against injury and violence, as for his repose.”

Semayne’s Case, 77 Eng. Rep. 194, 195 (K.B. 1604)

(footnote omitted). Outside of a few narrow and welldefined exigent circumstances, forcibly entering a

home was “regarded as an unlawful search or seizure.”

Houghton, 526 U.S. at 299. The common law afforded

no authority at all for warrantless entry merely to

search a home. And even search warrants were available only to recover stolen goods. See Davies, supra,

at 645-46.

“The Fourth Amendment embodies this centuriesold principle of respect for the privacy of the home.”

Wilson v. Layne, 526 U.S. 603, 610 (1999). Its text explicitly links “houses” with “the right of the people to

be secure.” U.S. Const. amend. IV. And its broad protections for personal security were largely a response

to abusive home searches the Founding generation

suffered under British rule—namely, searches conducted under “general warrants” and “writs of assistance” that were not based on sworn evidence or individualized suspicion. See 3 Joseph Story, Commentaries on the Constitution of the United States 748,

§ 1895 (1833) (attributing the Fourth Amendment to

“the strong sensibility excited, both in England and

America, upon the subject of general warrants”).

“Opposition to such searches was in fact one of the

driving forces behind the Revolution itself.” Riley v.

California, 573 U.S. 373, 403 (2014). In the mid-1700s,

general warrants were used in both England and

America to conduct unrestrained searches of homes.

Because of the common law’s strong protections for the

home, the British government was forced to enact statutes abrogating those safeguards. See Davies, supra,

at 646. For example, Parliament enacted the “Act of

Frauds” in 1662, which empowered officials to “enter,

and go into any house, shop, cellar, warehouse or room,

or other place, and in case of resistance, to break open

doors, chests, trunks and other package, there to seize,

and from thence to bring, any kind of goods or merchandize whatsoever, prohibited and uncustomed.”

Act of Frauds of 1662, 12 Car. 2, cl. 11, § V(2), reprinted in 8 The Statutes at Large of England and

Great-Britain 78, 81 (1763). The Act also authorized

the use of writs of assistance, which permitted officers

to “commandeer anyone—constables and ordinary citizens alike—to help in executing searches and seizures.” Hon. M. Blane Michael, Reading the Fourth

Amendment: Guidance from the Mischief That Gave It

Birth, 85 N.Y.U. L. Rev. 905, 907 (2010).

Colonial opposition to general warrants and writs

of assistance was galvanized by events on both sides of

the Atlantic in the years before the American Revolution. After King George II died in 1760, colonial

customs officers had to reapply for writs of assistance

to be issued in the name of the new king. Id. at 908.

In Boston, where the economy depended in part on

trade in smuggled goods, a group of merchants objected to the new king’s writs in Paxton’s Case. See id.

Their attorney, James Otis, delivered a “declamation

against general warrants” widely considered “one of

the most celebrated orations in U.S. history.” Laura

K. Donahue, The Original Fourth Amendment, 83 U.

Chi. L. Rev. 1181, 1249 (2016). Otis called the writ of

assistance “the worst instrument of arbitrary power,”

placing “the liberty of every man in the hands of every

petty officer,” for it permitted officers to invade private

homes “when they please[, and] we are commanded to

permit their entry.” 2 Works of John Adams, app. A at

523-24 (Charles Francis Adams ed., 1850). Otis thus

advanced the bedrock principle “that a person’s home

is especially private and must be protected from arbitrary government intrusion.” Michael, supra, at 90809. And his challenge to writs of assistance “was perhaps the most prominent event which inaugurated the

resistance of the colonies to the oppressions of the

mother country.” Boyd v. United States, 116 U.S. 616,

625 (1886).

Although Otis failed to prevent the issuance of the

writs he fought in Boston, English courts promptly

vindicated his arguments in a series of cases arising

out of the Crown’s use of general warrants to silence

John Wilkes and other political enemies of King

George III. As one landmark decision put it, such “discretionary power . . . to search wherever [the officers’]

suspicions may chance to fall” would “affect the person

and property of every man in this kingdom, and is totally subversive of the liberty of the subject.” Wilkes v.

Wood, 19 How. St. Tr. 1153, 1167 (C.P. 1763). “[L]egal

criticism of the general warrant was especially strong

when the security of a house was at issue.” Davies,

supra, at 603. One decision noted that if the government’s promiscuous warrants were permitted, every

Englishman could find that “[h]is house is rifled” and

“his most valuable secrets are taken out of his possession.” Entick v. Carrington, 19 How. St. Tr. 1029, 1064

(C.P. 1765).

These cases were widely covered in American

newspapers, and “the reaction of the colonial press to

that controversy was intense, prolonged, and overwhelmingly sympathetic to Wilkes.” Cuddihy, supra,

at 538. “[A]ccounts of the trials exclaimed the importance of the issue for English liberty and the sanctity of the house while condemning general warrants

as ‘illegal,’ ‘unconstitutional,’ ‘void,’ ‘oppressive,’ and

‘unwarrantable.’” Davies, supra, at 563 & n.22 (collecting sources).

After Independence, the fight to preserve the

home’s security continued. While general warrants initially remained common, the “specific warrant ultimately won out.” Cuddihy, supra, at 602. By 1784,

eight states had “formulated constitutions with restrictions on search and seizure.” Id. at 603. When

the Constitutional Convention unveiled its proposed

new federal charter, critics expressed fears about the

use of general warrants to ransack homes. Patrick

Henry raised the specter of federal officers “who may

search, at any time, your houses, and most secret recesses.” 3 The Debates in the Several State Conventions on the Adoption of the Federal Constitution 58

(Jonathan Elliot ed., 1836). Another Anti-Federalist

protested that officers would have “power to enter your

houses at all times, by night or day, and if you refuse

them entrance, they can, under pretense of searching

for excisable goods, . . . break open your doors, chests,

trunks, desks, and boxes, and rummage your houses

from bottom to top.” Essay by a Farmer and Planter,

Md. Journal, Mar. 27, 1788, in 5 The Complete AntiFederalist 74-75 (Herbert J. Storing ed., 1981). The

sister of James Otis, Mercy Otis Warren, argued for a

constitutional guarantee to prevent “any petty revenue officer” from “enter[ing] our houses, search[ing],

insult[ing], and seiz[ing] at pleasure.” A Columbian

Patriot, Observations on the New Constitution, and on

the Federal and State Conventions, reprinted in Pamphlets on the Constitution of the United States 13 (Paul

Leicester Ford ed., 1888).

To assuage these fears, state ratifying conventions

demanded more explicit protection from unbridled

search and seizure. For example, Virginia’s proposed

federal bill of rights provided that “all general warrants to search suspected places, or to apprehend any

suspected person, without specially naming or describing the place or person, are dangerous and ought not

to be granted.” Cuddihy, supra, at 684. Other states

mimicked this language. Id. at 685. Arguments about

the dangers of general warrants received extensive

press coverage, illustrating “a consensus for a comprehensive right against unreasonable search and seizure.” Id. at 686.

Two key themes emerged from these debates: the

idea that the right of personal security is at its peak

within the four walls of the home, and the strongly felt

need for a limiting principle to regulate the discretion

of officers engaged in searches that encroach on that

security. These ideas found expression in James Madison’s draft of the Fourth Amendment, which made

clear the importance of credible evidence and individualized suspicion as predicates for home searches:

“The rights of the people to be secured in their persons;

their houses, their papers, and their other property,

from all unreasonable searches and seizures, shall not

be violated by warrants issued without probable cause,

supported by oath or affirmation, or not particularly

describing the places to be searched, or the persons or

things to be seized.” 1 Annals of Cong. 452 (1789) (Joseph Gales ed., 1834). As the Amendment’s language

took final form, its explicit recognition of the home’s

sanctity and its requirement of specific warrants remained materially the same. Cuddihy, supra, at 69597.

The Fourth Amendment thus enshrines in our national charter the Framers’ opposition to searches and

seizures, especially within the home, conducted without particularized suspicion backed by reliable evidence. A key feature of the Framers’ response, as discussed next, was the requirement of probable cause.

III. The Framers Viewed Probable Cause as a

Vital Safeguard Against Unfounded

Searches and Seizures.

While the Fourth Amendment mentions probable

cause only in its Warrant Clause, the Framers understood that standard to be a more general safeguard

against unreasonable searches and seizures, whether

or not conducted with a warrant. Given the home’s

special status under common law and in the Fourth

Amendment’s history, the Framers would not have

sanctioned home entry with anything less than probable cause.

The concept of probable cause developed “long before the creation of either general or specific warrants.” Tracey Maclin, The Complexity of the Fourth

Amendment: A Historical Review, 77 B.U. L. Rev. 925,

961 (1997). Sometimes referred to as “just” or “good”

cause for “belief” or “suspicion,” probable cause arose

to regulate arrests “in a warrantless world.” Andrew

E. Taslitz, Reconstructing the Fourth Amendment: A

History of Search and Seizure, 1789–1868, at 46

(2006). The concept has always centered around “individualized suspicion supported by quality evidence.”

Id.

As early as 1244, a bare accusation of murder was

ruled inadequate—to have given “no cause”—for an arrest under English common law. Jack K. Weber, The

Birth of Probable Cause, 11 Anglo-Am. L. Rev. 155, 156

(1982). In 1326, the King’s Bench similarly ruled that

the cause for which a person was arrested “seems . . .

insufficient.” R. v. de Wellingborough (K.B. 1326), in

4 Select Cases in the Court of King’s Bench Under Edward II, at 164-65 (G.O. Sayles ed., 1957). Forty years

later, an arrest of suspected robbers was held unjustified because it was based only on “common cry and

scandal.” Ughtred v. Musgrave (King’s Council, 1366),

in Select Cases Before the King’s Council, 1243–1482,

at 60 (I.S. Leadam ed., 1918); see Cuddihy, supra, at

423. As these cases illustrate, anyone who arrested a

supposed felon without a warrant (as both private citizens and public officers could do) acted “at his peril,”

and if sued would have to justify the cause for the arrest. 2 Frederick Pollock & Frederic William Maitland, The History of English Law Before the Time of

Edward I, at 582-83 (2d ed. 1898). Although “virtual

certainty” was not required, at least “a moderate degree of suspicion” was necessary. Weber, supra, at

159.

Describing probable cause, Henry de Bracton’s

treatise discussed the reliability of the informer, the

value of the evidence, and the extent of any corroboration, such as “a precedent act” by the suspect. See

2 Bracton on the Laws and Customs of England, supra,

at 403-04. Sensible inferences could be drawn, “as

where one is taken over the body of the dead man with

his knife dripping blood,” but rumor alone could not

create a presumption of suspicion unless it came from

“worthy and responsible men, . . . and it must be not

once but repeatedly that complaint arises.” Id. at 404.

“For,” the treatise cautioned, “uproar and public outcry are at times made of many things which in truth

have no foundation.” Id.

By the late fifteenth century, anyone who personally knew of a felony could arrest the suspected culprit,

but “[s]uch suspicions required good evidence.”

Shapiro, supra, at 129. This restriction applied to law

enforcement officers, although their “grounds of suspicion might be less certain than those of the private citizen.” Id.

Probable cause came into sharper focus with the

proliferation of justice-of-the-peace manuals in the sixteenth century. Id. “These handbooks, from their inception, included a list of the ‘causes of suspicion,’” including a suspect’s “ability to commit the crime, his

whereabouts at the time of the crime, the presence of

witnesses and/or signs (for example, blood) that engender suspicion.” Id. Some of these criteria, such as a

suspect’s reputation and parentage, reflected a closeknit, class-stratified society, and plainly have not

stood the test of time. But what endured was the basic

idea of standards to “insure accusations had some rational basis,” without requiring accusers “to fully

prove their suspicions.” Id. at 130. These standards

regulated warrantless intrusions as well as the issuance of warrants.

For instance, Michael Dalton’s Country Justice,

“[t]he most influential seventeenth-century handbook

in both England and America,” Taslitz, supra, at 47,

instructed that warrantless arrests required “some

just cause, or some lawful and just suspicion at the

least,” Dalton, supra, at 447. The accuser making the

arrest needed a basis for his belief, id. at 447-49,

though again, some of the accepted bases like “the

common voice and fame” would not persist. William

Sheppard similarly endorsed warrantless arrests if a

person had “some cause and reason to suspect th[e]

party that he doth arrest,” while warning that

“whether the cause of suspicion be good, shall be tried

by the judges in [an] action of false imprisonment.”

Sheppard, Epitome, supra, at 650. And indeed, court

decisions fleshed out criteria that qualified as “good

causes of suspicion.” Sir Anthony Ashley’s Case, 77

Eng. Rep. 1366, 1368 (St. Ch. 1611) (listing examples,

including “if murder be committed, and one is seen

near the place”). These criteria largely centered

around “behavior reasonably suggesting guilt.” Cuddihy, supra, at 423.

By the time of the great common law treatises

known to the American Founders, probable cause was

more clearly identified as an evidentiary threshold distinct from the concept of suspicion. Matthew Hale

wrote that accusers could make warrantless arrests

without fear of liability if they had “probable cause of

suspicion.” 1 Hale, supra, at 588. And if an accuser

sought a warrant, the justice of the peace was “a competent judge of the probabilities offered to him of such

suspicion.” 2 id. at 110. William Hawkins similarly

cautioned that someone making an arrest would have

to show the “cause which induced him to have such a

suspicion,” which must “appear to the court to have

been a sufficient ground for his proceeding.” 2 Hawkins, supra, at 121. The “common fame of the country,” for instance, was inadequate unless it were

shown, “upon evidence,” that “such fame had some

probable ground.” Id. at 119 (footnote omitted). Warrants could not be granted “without such a probable

cause, as might induce a candid and impartial man to

suspect the party to be guilty.” Id. at 136.

The treatises thus presented probable cause as

“credible evidence of facts giving rise to suspicion.”

Taslitz, supra, at 48. Hawkins’s treatment in particular “became a standard part of the arrest canon of the

English and the American handbook tradition.”

Shapiro, supra, at 138; see, e.g., Burn, supra, at 747

(parroting Hawkins’s “candid and impartial man” formulation of the probable cause standard). William

Blackstone confirmed that warrantless felony arrests

could be made “upon probable suspicion,” and that a

justice of the peace could issue arrest warrants based

on the reports of others, “because he is a competent

judge of the probability offered to him of such suspicion.” 4 Blackstone, supra, at 292, 290; see also

1 Chitty, supra, at 23 (stating that warrants required

“such a probable cause as might induce a discreet and

impartial man to suspect the party to be guilty”).

In “the controlling British precedent on probable

cause” at the Founding, Cuddihy, supra, at 583, the

King’s Bench held an excise officer liable in trespass

for initiating a fruitless home search for stolen goods,

because “no evidence was given at the trial of any probable cause or ground of suspicion,” Bostock v Saunders,

95 Eng. Rep. 1141, 1145 (K.B. 1773) (de Grey); see id.,

96 Eng. Rep. 539, 540 (K.B. 1773) (de Grey) (“[T]he

suspicion must be very well founded to justify entering

a house without the owner’s consent. Every man’s

house is his castle.”). And in Leach v. Money, one of

the seminal general-warrant cases, the plaintiff argued that the arresting officer had “no probable cause,

nor any reason for justifying the officer under a probable cause.” 19 How. St. Tr. 1001, 1022 (K.B. 1765).

“Whether there was a probable cause or ground of suspicion was a matter for the jury,” the court held, but

the warrant at issue was invalid because “the receiving or judging of the information [was] left to the

discretion of the officer.” Id. at 1026-27 (quotation

marks omitted); accord Entick, 95 Eng. Rep. at 818

(“there must be an oath that the party has had his

goods stolen, and his strong reason to believe they are

concealed in such a place” (emphasis added)).

“American trends concerning probable cause were

discernable by the 1760s,” at which point the colonists

understood probable cause “to include important guarantees of a sufficiently trustworthy evidentiary basis.”

Taslitz, supra, at 48-49. Probable cause was salient

whether or not a warrant was employed.

Americans condemned general warrants because

they facilitated searches that lacked probable cause

and rested only on “[b]are suspicion without oath.”

2 Works of John Adams, supra, at 524 (James Otis’s

speech); see supra Part II. At the same time, “warrantless seizures of ships stimulated the belief that seizures as well as searches were unreasonable without

adequate cause.” Cuddihy, supra, at 586. Under color

of statutory authority to seize ships based on probable

cause, the British captured American ships for alleged

customs violations, including John Hancock’s vessel,

the Liberty. A Boston town meeting denounced the

lack of “any probable cause of seizure that we know of.”

Id. at 589. A prominent Charleston shipowner likewise protested that there was “no shadow of pretense”

of any cause for seizing his ship. Id. at 587. “The statements on probable cause [in these two cases] saturated

newspapers from Rhode Island to South Carolina.” Id.

at 590; see Thomas Barrow, Trade and Empire: The

British Customs Service in Colonial America, 1660–

1775, at 234 (1967) (“Hancock and his ship, the Liberty, had commenced a series of events leading to open

revolution.”). This controversy “helped to focus colonial thinking on the principle of probable cause,”

Maclin, supra, at 962, and “inserted ‘probable cause’ of

seizure into the American legal vocabulary” as a rule

demanding a “substantial reason” for such actions,

Cuddihy, supra, at 591.

It was only natural, therefore, that after Independence many states enacted protections against

searches and seizures unsupported by adequate cause.

E.g., Mass. Const. art. XIV (1780) (safeguarding the

“right to be secure from all unreasonable searches and

seizures . . . if the cause or foundation of them be not

previously supported by oath or affirmation”). These

provisions used a variety of formulations: some proscribed seizures of persons “whose offense is not . . .

supported by evidence,” Va. Decl. of Rights § 10 (1776),

while others prohibited warrants that lacked “a sufficient foundation for them,” Pa. Const. of 1776, Decl. of

Rights, art. X. Like the Fourth Amendment, however,

they all reflected the basic idea that reasonable

searches and seizures must be based on good cause.

After ratification, the First Congress confirmed

the prevailing view that probable cause was an important safeguard for searches and seizures, regardless of whether a warrant was involved. Less than two

months before sending the Fourth Amendment to the

states for approval, Congress enacted a customs statute that relied on probable cause for searches conducted both with and without warrants. The statute

permitted customs officials to search ships without a

warrant if they had “reason to suspect” that dutiable

goods were concealed inside. Act of July 31, 1789,

ch. 5, § 24, 1 Stat. 29, 43. Likewise, customs officials

could search dwellings and other buildings on land—

with a warrant—if they had “cause to suspect” the concealment of dutiable goods. Id. There is no indication

that these two formulations (“reason to suspect” and

“cause to suspect”) were originally understood as different standards; instead, the distinction was whether

or not a warrant was required. Indeed, the statute immunized customs officials from liability for seizures in

both contexts if a judge found there was “a reasonable

cause of seizure.” Id. § 36, 1 Stat. at 47. These three

formulations all meant the same thing—and as evident in the provision authorizing search warrants,

they were understood as equivalent to the “probable

cause” that was soon to be inscribed in the Fourth

Amendment.

Similarly, the First Congress later authorized internal revenue inspectors to obtain search warrants

“upon reasonable cause of suspicion” that taxable

spirits were fraudulently concealed in a building—

yet another formulation expressing the same concept

of adequate cause. Act of Mar. 3, 1791, ch. 15, § 32,

1 Stat. 199, 207. Like customs officials, revenue inspectors were immune for their seizures if “there was

probable cause for making the said seizure.” Id. § 38,

1 Stat. at 208.6

In sum, from the era of Magna Carta in England

to the First Congress in America, the requirement of

probable cause (or “just” cause, or “reasonable” cause)

was seen as a valuable safeguard against unfounded

searches and seizures, even in contexts in which warrants were not needed. Of course, it is precisely in

those contexts—where officers act on their own initiative, without prior judicial approval—that this safeguard may be most valuable.

6 Separately, this statute allowed entry into distilleries for the

limited purpose of cataloguing the liquor stored there, but only

after an owner registered the premises with the government as a

distillery. See id. §§ 25-26, 29, 1 Stat. at 205-06.

CONCLUSION

For the foregoing reasons, the judgment of the

court of appeals should be reversed.

Respectfully submitted,

ELIZABETH B. WYDRA

BRIANNE J. GOROD*

BRIAN R. FRAZELLE

MIRIAM BECKER-COHEN

CONSTITUTIONAL

ACCOUNTABILITY CENTER

1730 Rhode Island Ave. NW

Suite 1200

Washington, D.C. 20036

(202) 296-6889

brianne@theusconstitution.org

Counsel for Amicus Curiae

August 6, 2025

* Counsel of Record

This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.