This chapter defends a surprising implication of the causal theory of perception: we see silhouetted objects by virtue of seeing their back surfaces. The primacy of surfaces is reviewed to support the principle that we see opaque objects by seeing their surfaces. Since the front surface of a silhouetted object is idle, the causal theory rules out the possibility that we see silhouettes by seeing their front surfaces. Only back surfaces are available.
Keywords: surface, causal, silhouette, opaque