Abstract：Communism is the unity of scientific truth and value ideal. From the theory of Wittgenstein's demarcation between “the declarable”and “the unspeakable”, and with the logic boundary of“the state of affairs”and “non-exact state of affairs”, the scientific truth of communism is strengthened and the original mission of communism revisited. The historical inevitability and programmatic principles of communism realization are“declarable”and can be clearly stated, as well as its historical transcendence over capitalism. When the communism will be realized, what the specific scheme is, and what the society will be like after its realization are generally “unspeakable”. The “unspeakable”future requires today's generation to remain silent but future generations to write up for it based on the development of society.

Keyword：communism;Tractatus Logico-Philosophicus;the declarable;the unspeakable;