Final answer:
The idea that each spoken sentence may be novel arises from the intrinsic variability of language and its use in unique contexts. Theories like Sapir-Whorf hypothesis and the context-dependent nature of language by Wittgenstein support this view, as does the creation of new expressions.
Step-by-step explanation:
The psychological idea that every sentence we speak is novel and has a high probability of never having been spoken before is rooted in the dynamic nature of language and the infinite combinations of words possible. This notion suggests that individual experience and situational context give rise to unique linguistic expressions. The probability of producing an entirely novel sentence is due to the personal, cultural, and contextual variability inherent in language use. Certain linguistic theories, such as those proposed by Edward Sapir and Benjamin Whorf, express that language not only communicates experiences but also shapes our perception of reality. Ludwig Wittgenstein's philosophy indicates that language's meaning is context-dependent, which supports the view that our spoken sentences could be novel due to the distinctive circumstances of their use. Moreover, the act of coining new expressions or words, as poets and writers often do, contributes to the endless creative potential of language.