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TWITTER, INC. v. TAAMNEH 

Syllabus 

actionable wrong—here, an act of international terrorism.  However, 
that  does  not  require  a  strict  nexus  between  the  assistance  and  the 
wrongful act; defendants are liable for other torts that are the foresee-
able risk of an intended tort, and an aider and abettor can assist some-
one without knowing all the details of his plan.  Plus, in appropriate
circumstances, a defendant’s role in an illicit enterprise can be so sys-
temic and intentional that the defendant aids and abets each act of the 
enterprise—as in Halberstam itself. 

To summarize the requirements of §2333(d)(2), the phrase “aids and 
abets, by knowingly providing substantial assistance” points to the el-
ements  and  factors  articulated  by  Halberstam.  Those  elements  and 
factors  should  not  be  taken  as  inflexible  codes  but  should  be  under-
stood in light of the common law and applied as a framework designed 
to hold defendants liable when they consciously and culpably “partici-
pate[d] in” a tortious act in such a way as to help “make it succeed.” 
Nye & Nissen v. United States, 336 U. S. 613, 619.  Pp. 17–21. 

(c)  Plaintiffs have satisfied Halberstam’s first two elements by al-
leging  both  that  ISIS  committed  a  wrong and  that  defendants  knew 
they were playing some sort of role in ISIS’ enterprise.  But plaintiffs’ 
allegations do not show that defendants gave such knowing and sub-
stantial assistance to ISIS that they culpably participated in the Reina
attack.  Pp. 21–30.

(1) Plaintiffs allege that defendants aided and abetted ISIS in the 
following ways: First, they provided social-media platforms, which are 
generally available to the internet-using public; ISIS was able to up-
load content to those platforms and connect with third parties on them.
Second,  defendants’  recommendation  algorithms  matched  ISIS-re-
lated content to users most likely to be interested in that content.  And, 
third, defendants knew that ISIS was uploading this content but took
insufficient steps to ensure that its content was removed.  Plaintiffs do 
not allege that ISIS or Masharipov used defendants’ platforms to plan 
or coordinate the Reina attack.  Nor do plaintiffs allege that defend-
ants gave ISIS any special treatment or words of encouragement.  Nor 
is there reason to think that defendants carefully screened any content
before allowing users to upload it onto their platforms.

None of plaintiffs’ allegations suggest that defendants culpably “as-
sociate[d  themselves]  with”  the  Reina  attack,  “participate[d]  in  it  as
something  that  [they]  wishe[d]  to  bring  about,”  or  sought  “by  [their] 
action to make it succeed.”  Nye & Nissen, 336 U. S., at 619 (internal 
quotation marks omitted).  Defendants’ mere creation of their media 
platforms is no more culpable than the creation of email, cell phones, 
or  the  internet  generally.  And  defendants’  recommendation  algo-
rithms are merely part of the infrastructure through which all the con-
tent on their platforms is filtered.  Moreover, the algorithms have been