Quine's Empiricism

As an empiricist I continue to think of the conceptual scheme of science as a tool, ultimately, for predicting future experience in the light of past experience. 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 . . . 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. Both sorts of entities enter our conceptions only as cultural posits.

In his book from which you quote, Quine rejects the analytic (true by the meaning of the words) -synthetic (true by virtue of facts) distinction. The fact of a physical object is not subject to falsifiability while theories that contain those facts are. I think Quine is suggesting a cautious or humble approach to facts as the selection of those facts may be just as dubious as the theory that Thor controls thunder.