 The thick distinction divides the subjective and objective components of sense perception. As Shepherd notes, philosophers take very different views on this division, citing Malebranche, Leibniz, Reid, and Berkeley. She contends that we tend to adhere to the inner-outer distinction just described because it is produced by the natural mental activity of making causal inferences from the perception that sensations begin to appear in consciousness. In this sub-section, we consider the details of the origin of this inner-outer distinction and belief in the external existence of sensible objects. 