How do we learn, use, and understand the meaning of words representing sensations? How is the connection between words and sensations structured? How can outward signs of sensations be manifested? What does it mean “to understand someone”? Is semantics affected by inner states? What does one mean when one uses an expression to describe a sensation? How should such success in communication be defined? Grammar, Expressiveness, and Inter-subjective Meanings: Wittgenstein’s Philosophy of Psychology deals with these questions, examining the peculiar uses of language-games representing sensations (such as “thinking”, “seeing such-and-such”, and “I’m in pain”) and exploring outer references to inner states. Externalising something internal gives expression to the psychological experience. As such, an expression should be understood as a sophisticated form of exteriorising experiences. This book clarifies the use of sense-expressions and the praxis of “bringing to expression” as an inter-subjective meaning process. The central focus of the book entails both the outwardness of language and the inwardness of experience, as was intensively remarked by Wittgenstein’s last writings (namely his lectures from 1946–47, exclusively and remarkably concerning the philosophy of psychology), which were recently published and which, despite their importance and originality, are still little known.