Each of us is uniquely subject to certain kinds of stimulation from a small part of the universe within our skins. Mentalistic psychologies insist that other kinds of events, lacking the physical dimensions of stimuli, are accessible to the owner of the skin within which they occur. One solution often regarded as behavioristic, granting the distinction between public and private events and ruling the latter out of consideration, has not been successful. A science of behavior must face the problem of privacy by dealing with events within the skin in their relation to behavior, without assuming they have a special nature or must be known in a special way.

The search for copies of the world within the body (e.g. the sensations and images of conscious content) has also had discouraging results. The organism does not create duplicates: Its seeing, hearing, smelling, and so on are forms of action rather than of reproduction. Seeing does not imply something seen. We know that when we dream of wolves, no wolves are actually there; it is harder to understand that not even representations of wolves are there.

Mentalistic formulations create mental way stations. Where experimental analyses examine the effects of variables on behavior, mentalistic psychologies deal first with their effects on inferred entities such as feelings or expectations and then with the effects of these entities on behavior. Mental states thus seem to bridge gaps between dependent and independent variables, and mentalistic interpretations are particularly attractive when these are separated by long time periods. The practice confuses the order of events and leads to unfinished causal accounts.