William James's concept “stream of thought” has mainly two backgrounds to build up its original style. The first is the difference between material state and inner state of vital phenomena, and the second is the impossibility to associate plural ideas without transcendental subject. The first is influenced by an issue in the theory of evolution. That is a question, on which point in evolution the inner state of life has emerged. This is the principal impossibility which is contrary to the emergence of vital phenomena as material body. For this problem James reexamines “mind-stuff theory”, and he approves its one aspect which assumes inner state from the beginning of evolution, but rejects its another aspect which affirms association. The problem of the latter aspect has something to do with the second background. To overcome this problem, James attained to “stream” after examining “several another hypotheses”.