Physical objects are conceptually imported into the situation as convenient intermediaries — not by definition in terms of experience, but simply as irreducible posits, comparable, epistemologically, to the gods of Homer.
Let me interject that for my part I do, qua lay physicist, believe in physical objects and not in Homer’s gods; and I consider it a scientific error to believe otherwise. But in point of epistemological footing the physical objects and the gods differ only in degree and not in kind.
Quote from W.V.O. Quine, “Two Dogmas of Empiricism”, From a Logical Point of View (Harvard University Press, 1953; second, revised, edition 1961)