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20 

TWITTER, INC. v. TAAMNEH 

Opinion of the Court 

to  the  next  problem:  As  Halberstam  makes  clear,  people
who  aid  and  abet  a  tort  can  be  held  liable  for  other  torts 
that  were  “a  foreseeable  risk”  of  the  intended  tort.    705 
F. 2d, at 488.  Accordingly, a close nexus between the assis-
tance and the tort might help establish that the defendant
aided and abetted the tort, but even more remote support
can still constitute aiding and abetting in the right case.

Moreover, in appropriate circumstances, a secondary de-
fendant’s role in an illicit enterprise can be so systemic that 
the  secondary  defendant  is  aiding  and  abetting  every
wrongful  act  committed  by  that  enterprise—as  in  Hal-
berstam itself.  Id., at 487–488.  At this point, aiding-and-
abetting  liability  begins  to  blur  with  conspiracy  liability, 
which typically holds co-conspirators liable for all reasona-
bly  foreseeable  acts  taken  to  further  the  conspiracy.    See 
Pinkerton v. United States, 328 U. S. 640, 647–648 (1946); 
see also Halberstam, 705 F. 2d, at 482–483 (noting the oc-
casional overlap).  Yet, as noted above, aiding and abetting 
lacks the requisite agreement that justifies such extensive
conspiracy  liability.    See  Restatement  (Second)  of  Torts 
§876, Comment a, at 316 (“The theory of the early common
law was that there was mutual agency of each [conspirator] 
to act for the others”); Pinkerton, 328 U. S., at 646.  Thus, 
while  the  facts  of  Halberstam  are  not  totemic  (lest  courts 
strain to compare Linda Hamilton with international crim-
inal  syndicates),  its  facts  are  useful  when  determining 
whether a defendant has so consciously “participate[d] in” 
a  series  of  tortious  acts  in  order  to  “make  [each  one]  suc-
ceed.”  Nye & Nissen, 336 U. S., at 619 (internal quotation 
marks omitted). 

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To  summarize  the  requirements  of  §2333(d)(2),  the
phrase “aids and abets, by knowingly providing substantial 
assistance,” points to the elements and factors articulated 
by Halberstam.  But, those elements and factors should not 

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