6 TWITTER, INC. v. TAAMNEH Syllabus of mind with respect to their actions and the tortious conduct (even if not always the particular terrorist act). Finally, the Ninth Circuit appears to have regarded Halberstam’s six substantiality factors as a sequence of disparate, unrelated considerations without a common conceptual core. In doing so, the Ninth Circuit focused primarily on the value of defendants’ platforms to ISIS, rather than whether defendants culpably associated themselves with ISIS’ actions. Pp. 27–29. (3) There is also one set of allegations specific to Google: that Google reviewed and approved ISIS videos on YouTube as part of a revenue-sharing system and thereby shared advertising revenue with ISIS. But the complaint here alleges nothing about the amount of money that Google supposedly shared with ISIS, the number of accounts approved for revenue sharing, or the content of the videos that were approved. Nor does it give any other reason to view Google’s revenue sharing as substantial assistance. Without more, plaintiffs thus have not plausibly alleged that Google knowingly provided substantial assistance to the Reina attack, let alone (as their theory of liability would require) every single terrorist act committed by ISIS. Pp. 29– 30. (d) The concepts of aiding and abetting and substantial assistance do not lend themselves to crisp, bright-line distinctions. Applying the guideposts provided by the common law and Halberstam, the nexus between defendants and the Reina attack is far removed. As alleged by plaintiffs, defendants designed virtual platforms and knowingly failed to do “enough” to remove ISIS-affiliated users and ISIS-related content from their platforms. Yet, plaintiffs have failed to allege that defendants intentionally provided any substantial aid to the Reina attack or otherwise consciously participated in it—much less that defendants so pervasively and systemically assisted ISIS as to render them liable for every ISIS attack. Plaintiffs accordingly have failed to state a claim under §2333(d)(2). Pp. 30–31. 2 F. 4th 871, reversed. THOMAS, J., delivered the opinion for a unanimous Court. JACKSON, J., filed a concurring opinion.