 The immediate description of the perceptual world is in terms of enduring objects, their properties and relationships, and that description is only probable. The world can be described egocentrically in terms of “impressions” and “sense data,” but, Reichenbach argues, ordinary descriptions of things are not equivalent to egocentric descriptions in terms of impressions, because, however elaborate, egocentric formulations do not entail object claims, they only confer a probability on object descriptions, (and, of course, in parallel, given Reichenbach’s anti-foundationalism, egocentric descriptions are only probable). The argument is not in accord with Reichenbach’s own criterion for equivalent descriptions, but the conclusion is repeatedly emphasized. Reichenbach insists, sometimes in rather sharp language, that the logical positivists and unnamed “pretentious” logicians are simply wrong about locating the foundations of knowledge in sense data or analytical truths. 