Defamation law has long treated three roles differently: the primary publisher who writes or exercises editorial control over defamatory content, the secondary distributor who circulates content authored by others (a bookstore or newsstand, for example), and the mere conduit who merely and passively transmits content with essentially no ability to review or control it, such as a telephone carrier or a mail service. The mere conduit sits at the bottom of that hierarchy, and generally faces liability only in narrow circumstances, if at all.

The defense has taken on outsized importance in the internet era, where platforms carrying enormous volumes of third-party content argue they function as conduits rather than publishers. In the United States, that argument is now often overtaken entirely by a statutory immunity -- Section 230 of the Communications Decency Act -- that is broader than the common-law conduit defense and has become the primary battleground for online defendants, leaving the common-law doctrine most active today in offline distribution disputes.

A primary publisher -- an author, editor, or broadcaster who exercises editorial judgment over content -- bears the fullest exposure, generally without any need to prove the publisher knew the content was false. A distributor, such as a library, bookstore, or newsstand, occupies a middle tier: liability attaches only upon proof that the distributor knew or had reason to know the content was defamatory, not merely upon distributing it.

A true mere conduit sits below even the distributor tier -- a role involving essentially passive, mechanical transmission with no realistic opportunity to review content before it moves through the system. Some courts treat conduits as functionally immune from defamation liability regardless of after-the-fact knowledge, given the nature of the role, distinguishing them sharply from distributors who at least have some practical opportunity to screen what they circulate.

Courts distinguishing these tiers look at the degree of editorial control or judgment actually exercised, whether the party had actual knowledge or reason to know of the defamatory content, and whether the party's role involved one-time passive transmission or ongoing distribution with a real opportunity for review.

For online content, Section 230 of the Communications Decency Act generally treats providers of an interactive computer service as not the publisher or speaker of content created by someone else, which is a broader shield than the common-law conduit defense -- it can apply even where a platform has some ability to review content, and even where it has knowledge of specific defamatory posts, so long as the platform did not itself create or materially contribute to the content. That statutory immunity has largely displaced common-law conduit analysis for internet platforms, though the common-law framework still governs offline distributors and any content a platform itself authors or materially shapes.

A plaintiff seeking to hold a distributor liable proves actual or constructive knowledge with evidence like prior complaint notices, takedown requests the distributor ignored, or other red flags a reasonable distributor would have acted on. A defendant asserting mere conduit status proves it with evidence of a purely mechanical, passive transmission role, an absence of editorial function, and a genuine lack of practical ability to screen the content passing through.

For an online defendant, Section 230 immunity is typically raised as a threshold, often dispositive defense that can end the case before the common-law publisher-distributor-conduit analysis is ever reached, provided the content in question was created by a third party rather than the platform itself.

In Juricratic, defamation defendants are modeled along an ordinal tier dial -- publisher, distributor, or conduit -- each carrying a different modeled exposure curve, with a separate binary statutory-immunity gate available for online defendants that, when it applies, can zero out exposure regardless of where the party otherwise sits on the tier dial.

War-gaming a matter with an online distribution component should test the case with the immunity gate both open and closed, since a Section 230 dismissal and a common-law conduit or distributor win can look identical in outcome but rest on entirely different legal grounds -- a distinction that matters for appeal risk and for how the case would play out against a similarly situated offline defendant.