Petitioner was convicted of violating the so-called membership clause of the Smith Act, which makes a felony the acquisition or holding of membership in any organization which advocates the overthrow of the Government of the United States by force or violence, knowing the purpose thereof. Held: The judgment is reversed, because the evidence was insufficient to prove that the Communist Party presently advocated forcible overthrow of the Government, not as an abstract doctrine, but by the use of language reasonably and ordinarily calculated to incite persons to action, immediately or in the future. Pp. 291-300.

(a) In order to support a conviction under the membership clause of the Smith Act, there must be some substantial direct or circumstantial evidence of a call to violence now or in the future which is both sufficiently strong and sufficiently pervasive to lend color to the otherwise ambiguous theoretical material regarding Communist Party teaching and to justify the inference that such a call to violence may fairly be imputed to the Party as a whole, and not merely to some