Reason, Truth and History

Putnam imagines that all sentient beings are brains in a vat fed experiences by a computer. His argument relies on a causal theory of reference: a word refers only to things with which its users have an appropriate causal connection. A vat-brain's word 'vat' would therefore refer to images or program features, not to real vats, so the sentence 'I am a brain in a vat,' when uttered by a vat-brain, would be false. Hence we can know we are not envatted. The argument is better understood as a case about the limits of reference than as a direct refutation of skepticism, and critics have debated its force.

Metaphysical realism holds that the world consists of mind-independent objects and that truth is correspondence between a theory and that fixed totality. Internal realism holds that asking which objects exist or what a term refers to makes sense only within a theory or conceptual scheme. Truth is then idealized rational acceptability: what would be justified under sufficiently good epistemic conditions. Putnam insists this is not relativism, since not every scheme is equally good and experience constrains inquiry. He later regarded internal realism as still tainted by a residual dualism and moved toward natural realism, so readers should treat it as a stage in his development.

The argument starts from a technical result: a consistent theory with an infinite model has many models, so its sentences can be reinterpreted while every one remains true. Applied to an ideal theory meeting every operational and theoretical constraint, this suggests that nothing in the theory or in our use of it selects the intended interpretation. Putnam concludes that the realist's unique correspondence between words and things is unavailable. David Lewis replied that natural properties are privileged candidates for reference, which rules out gerrymandered interpretations; Putnam answered that this adds more theory open to the same reinterpretation.

Putnam and Richard Rorty both reject the God's-eye view and both draw on pragmatist themes, but they diverge on what follows. Rorty argues that truth is best replaced by solidarity or what our peers let us say. Putnam holds that a notion of idealized rational acceptability preserves objectivity: we can criticize a community's practices from within inquiry and recognize that its present beliefs may be wrong. The disagreement between them is among the best known in late twentieth-century American philosophy, and later works such as Renewing Philosophy sharpen it.

Putnam argues that the dichotomy between facts and values is untenable because factual inquiry depends on epistemic values such as coherence, simplicity, and plausibility. If rational scientific inquiry already involves evaluation, then objectivity cannot be reserved for what science describes, and ethical claims need not be reduced to expressions of preference. He treats ethics as an area in which reasoned argument and revision are possible, without claiming that moral questions are as settled as empirical ones. This theme became central to his later writing on the entanglement of fact and value.

A frequent misreading takes Putnam to be an idealist or relativist who denies that a world exists independently of thought. He rejects both. His target is a particular philosophical picture: the idea that a single description of the world could be fixed independently of any conceptual contribution, and that truth is a relation between such a description and reality. He maintains that some descriptions are better than others, that experience limits what we may say, and that we can be mistaken. Reading the book as a denial of ordinary realism overlooks that distinction.