In this paper we investigate some of the uncouscious mechanisms underlying the process of acquisition of beliefs through perception. The paper outlines the basics of a formal theory of belief that is sensitive to the way in which beliefs are formed through perception. The process of belief acquisition involves a form of inference that is defeasible. We represent this kind of inference by means of well-known techniques of non-monotonic reasoning. In addition, we provides an account of perception that is consistent with the commonsense intuition for how perception functions, i.e., causality.