This paper proposes a framework that describes how musical form influences the probability relationship (PR), which was proposed in L. B. Meyer's Emotion and Meaning in Music (1956). First, his discussions about the style in Style and Music: Theory. History, and Ideology (1989) needs to be reconstructed based on the PR, because one can regard musical form as a kind of style. Second, along with the intraopus style and structure which Meyer suggested, a new pair, the extraopus style and structure, is indispensable to reexamine the musical form as ideal type, which is understood by the ideal auditor and in which the PR is considered static. Thus, it would be proved that the PR should also be divided into the dynamic and static one. Finally, this paper attempts to put the above arguments into practice, by describing the transition of the PR in the sonata form as an example.