Mind, Language and Reality (Philosophical Papers, Volume 2)

Putnam imagines a planet identical to Earth except that the clear drinkable liquid there has a different chemical composition, XYZ rather than H2O. An Earthling and a Twin Earthling may be in the same psychological state when each thinks about 'water', yet their words refer to different substances. Putnam concludes that meaning cannot be determined by psychological state alone, since the environment helps fix reference. The slogan he drew is that meanings are not in the head. The argument is the foundation of semantic externalism, and it has generated an enormous literature on whether mental content, and not just word meaning, is similarly environment-dependent.

Multiple realizability is the claim that the same mental state, such as pain, could be realized in physically very different systems, including humans, octopuses, or hypothetical machines. Putnam used it to attack type identity theory, associated with U. T. Place and J. J. C. Smart, which identifies each mental state type with a particular brain state type. If mental states can be realized in diverse physical ways, he argued, they must be individuated by functional role instead. This opened the way to functionalism and shaped cognitive science. Jaegwon Kim and others later challenged the argument, contending that it undermines the autonomy of the special sciences less than Putnam assumed.

Putnam eventually repudiated the position. In Representation and Reality he argued that functionalism cannot capture the content of propositional attitudes, since content depends on the environment and community, and that computational descriptions apply too liberally to be informative about minds. The reversal makes this volume a record of the founding statements of a view later criticized by its originator. Readers tracing the history of functionalism should read the early papers here beside the later book to see which arguments he kept, notably the externalism, and which he abandoned.

Putnam and Saul Kripke developed closely related views in the early 1970s: that terms such as 'gold' or 'water' refer to kinds whose essential nature is discovered empirically, and that reference is fixed by causal connection to samples, not by a description in the speaker's head. Putnam added the notion of a division of linguistic labor, according to which ordinary speakers defer to experts about what the term applies to. The overlap is often described as the Kripke-Putnam causal theory of reference. The two arrived at their positions independently and with different emphases, so it is best to treat them as parallel developments.

Putnam observes that most speakers cannot tell an elm from a beech, yet their use of 'elm' still refers to elms. Reference in such cases is fixed partly by the knowledge of experts in the community on whom ordinary speakers rely. Meaning is therefore a social phenomenon and not purely a matter of one speaker's mental state. Tyler Burge extended this style of argument to thoughts in his work on social externalism, as a result of which the Putnam-Burge line is often discussed together. Critics have asked how much of what we mean depends on deferential relations that speakers may not even recognize.

A frequent misreading takes the slogan to mean that thinking is not a brain process, or that meaning is something mysterious located outside the person. Putnam's claim is narrower: that a speaker's internal psychological state, narrowly individuated, does not by itself determine what the speaker's words refer to. The brain remains central to understanding and use, but reference also depends on the speaker's environment and linguistic community. Reading the thesis as a form of dualism or as skepticism about mental states misses its target, which is a particular internalist picture of how meaning is fixed.