How can two scientific theories make the same predictions while using different descriptions of reality?

Hilary Putnam argued that the same reality can be described in multiple ways, emphasizing that different scientific theories can be equivalent in their predictive and explanatory power despite utilizing different ontologies. For instance, one theory might describe phenomena using forces while another uses fields, yet both successfully account for the same observations.1

This phenomenon is closely related to the concept of underdetermination, which suggests that evidence may not uniquely determine a single theory. While some philosophers, such as W.V.O. Quine, proposed that it is always possible to maintain a hypothesis against any evidence, Putnam’s "internal realism" maintained that such equivalent descriptions do not lead to subjectivism or relativism. Instead, he argued that truth under a description is sufficient to avoid these pitfalls, rejecting the "metaphysical realist" view that requires a single, mind-independent correspondence between language and reality. By focusing on the autonomy of language and the practical success of theories, Putnam sought to reconcile the existence of multiple valid descriptions with an objective, realist understanding of the world.21