How does internal realism connect truth with ideal rational acceptability?

In philosophy, Hilary Putnam developed "internal realism" as a direct opposition to "metaphysical" or "external" realism. While metaphysical realism posits that truth is "radically nonepistemic"—meaning a theory could be perfectly rational yet still false—internal realism rejects this as a meaningless notion.12

Instead, internal realism connects truth to ideal rational acceptability. Under this view, truth is identified with what we would believe if we were to form our beliefs under evidentially ideal conditions. By linking truth to grounds for belief and rational justification, Putnam sought to avoid the skeptical pitfalls of metaphysical realism, which assumes a "ready-made world" independent of human thought.12

This approach shares affinities with Immanuel Kant’s transcendental idealism, as it eschews the idea of a reality "in itself" that exists beyond our descriptions. For Putnam, truth is "truth under a description," which allows for objective knowledge without requiring the problematic, mind-independent correspondence that he argued was impossible to sustain.12