What areas of philosophy did Hilary Putnam influence?

Hilary Putnam was a prominent American philosopher who made significant contributions across several core areas of philosophy, including metaphysics, epistemology, and the philosophies of mind, language, science, mathematics, and logic.31

His work is particularly noted for the following developments:

• Philosophy of Mind: He introduced functionalism, which defines mental states by their functional roles rather than their physical composition, and argued for the "multiple realizability" of mental states.2
• Philosophy of Language: He is widely recognized for semantic externalism, the view that linguistic meanings are not merely internal mental states but are connected to external reality.31
• Realism: Putnam maintained a persistent defense of realism, arguing that truth and knowledge are objective. He famously critiqued "metaphysical realism" and addressed skeptical challenges, such as the "brain in a vat" thought experiment, through his externalist framework.41
• Mathematics and Logic: He contributed to mathematical logic and, alongside W.V.O. Quine, proposed the "indispensability thesis," which argues that the reality of mathematical objects must be accepted because they are essential to our best scientific theories.45