Franz Brentano

German-Austrian philosopher who revived the scholastic concept of intentionality — the directedness of mental states toward objects — as the defining mark of the mental, founding phenomenology.

Intentionality is the mark of the mental: every mental state is about or directed toward an object (which may not exist). Mental phenomena are distinguished from physical phenomena by this directedness. Empirical psychology should study mental acts through inner perception. Inner perception is infallible — Brentano's foundationalism.