  Wilfred Sellars (1912–89), the distinguished philosopher, noted that a person may qualify as a behaviorist, loosely or attitudinally speaking, if they insist on confirming “hypotheses about psychological events in terms of behavioral criteria” (1963, p. 22).  A behaviorist, so understood, is someone who demands behavioral evidence for any psychological hypothesis.  For such a person, there is no knowable difference between two states of mind (beliefs, desires, etc.) unless there is a demonstrable difference in the behavior associated with each state.  Consider the current belief of a person that it is raining. If there is no difference in his or her behavior between believing that it is raining and believing that it is not raining, there is no grounds for attributing the one belief rather than the other.  The attribution is empirically empty or unconstrained. 