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Page Number: 3

Cite as:  598 U. S. ____ (2023) 

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Syllabus 

be accepted as immutable components” but should be “adapted as new 
cases  test  their  usefulness  in  evaluating  vicarious  liability.”    Id.,  at 
489.  Pp. 9–11.

(ii) Because  the  allegations  here—involving  international  ter-
rorist networks and world-spanning internet platforms—are a far cry 
from the facts of Halberstam, the Court must ascertain the basic thrust 
of Halberstam’s elements to determine how to adapt them to the facts 
of this case.  To do so, the Court turns to the common law of aiding and 
abetting upon which Halberstam rested, and to which JASTA’s com-
mon-law terminology points.  At common law, the basic “view of culpa-
bility” animating aiding and abetting liability is that “a person may be
responsible  for  a  crime  he  has  not  personally  carried  out  if  he  helps
another to complete its commission.”  Rosemond v. United States, 572 
U. S. 65, 70.  However, the concept of “helping” in the commission of a
crime or a tort has never been boundless and ordinarily requires some
level of blameworthy conduct; those limits ensure that aiding and abet-
ting does not sweep in mere passive bystanders or those who, for ex-
ample, simply deliver mail that happens to aid criminals.  In tort law, 
many  cases  have  thus  required  a  voluntary, conscious, and  culpable
participation in the wrongful conduct to establish aiding and abetting. 
In doing so, they further articulated Halberstam’s framework to cap-
ture those limits.  As above, that framework requires that the defend-
ant give knowing and substantial assistance to the primary tortfeasor; 
notably,  courts  often  viewed  those  twin  requirements  as  working  in
tandem, with a lesser showing of one demanding a greater showing of 
the  other  to  establish  a  conscious,  culpable  participation  in  the  tort. 
Pp. 11–16. 

(iii) Halberstam differentiated types of aid along the same cul-
pability axis that grounded the common law.  And its six factors for 
“substantial  assistance”  call  for  the  same  balancing  that  courts  had 
undertaken previously between the nature and amount of assistance
and the defendant’s scienter.  Pp. 16–17.

(2) The parties then vigorously dispute what precisely a defendant 
must aid and abet under §2333(d)(2).  Plaintiffs assert that it is “the 
person,” while defendants insist that it is the “act of international ter-
rorism.”  That syntactic dispute makes little difference here, because 
aiding and abetting is inherently a rule of secondary liability for spe-
cific wrongful acts.  In the tort context, liability is imposed only when 
someone commits (not merely agrees to commit) an actual tort.  And 
in this case, the ATA limits that liability to injuries caused by an “act 
of international terrorism,” §2333(a).  It thus is not enough for a de-
fendant to have given substantial assistance to a transcendent enter-
prise.  A defendant must have aided and abetted (by knowingly provid-
ing  substantial  assistance)  another  person  in  the  commission  of  the