  Skinner does not have much to say about just how inner (covert, private) behavior (like thinking, classifying, and analyzing) can be described in the same manner as public or overt behavior.  But his idea is roughly as follows.  Just as we may describe overt behavior or motor movement in terms of concepts like stimulus, response, conditioning, reinforcement, and so on, so we may deploy the very same terms in describing inner or covert behavior.  One thought or line of thought may reinforce another thought.  An act of analysis may serve as a stimulus for an effort at classification.  And so on.  Purely ‘mentalistic’ activities may be at least roughly parsed in terms of behavioral concepts — a topic to be revisited later in the entry (in the 7th Section). 