Goethe’s famous dictum, “In the beginning was the deed” is often invoked as a motto for behaviorism: if you want to understand the mind, you should look to overt behavior not to some supposed inner landscape. But that is not the only way the dictum can be interpreted, since not all deeds involve motions of the body—there are also mental deeds. There are intentional mental acts, such as remembering, imagining, and judging; these might be described as “mental behavior”—what the subject is doing mentally. This suggests the possibility of a distinctive new position in the metaphysics of mind—what I am calling “internal behaviorism”. It is not that I think this position is preferable to all others, or even that it is particularly plausible, but it is worth identifying it and exploring its contours. Think of this as a “research program”. So let’s examine its possible motivations and its strengths and weaknesses.
The idea is that mental actions are ontologically primary in the analysis of mind. We have mental states, mental traits, mental faculties, and mental systems, but all these are to be understood in terms of the mental actions associated with them. Following classic philosophical behaviorism, we could formulate the doctrine by saying that these mental entities are to be analyzed as dispositions to produce mental actions. For instance, beliefs are dispositions to make judgments, memories are dispositions to remember, and personality traits are dispositions to choose. We need not assume that all mental behavior is fully intentional: we can allow for sub-intentional mental acts or even reflexive mental acts—just as with bodily behavior broadly construed (“responses”). We could even extend the notion of behavior to include mental events of all kinds: then the doctrine will be that all mental notions are to be analyzed by reference to mental events. We could accordingly maintain that an emotional state like fear or anger is a disposition to experience suitable affective events such as feelings of fear or anger. Everything mental is bound up with mental events, many of them actions, and the mind is best understood from that basis. States, traits, faculties, and systems are all entities whose nature is constituted by the kinds of mental actions or events associated with them—by the mental deeds to which they are tied. What the mind does is key to what the mind is.
This kind of behaviorism might be part of a general metaphysical preference for events over other entities (substances, objects, properties) or it might be a doctrine specifically about the mind, holding that the mental is distinctively constituted by mental activity. Descartes viewed the mind as a mental substance imbued with mental attributes; on the behaviorist view (external or internal) it is better seen as a locus of action—a collection of animated events. Hitherto this metaphysical picture has been expressed in terms of bodily action, but that is not the only way to go: we can hold that the mind is essentially a site of mental activity—engaged not passive, flowing not fixed. There can be no mind where there is no mental behavior. What is an intention if not a disposition to form specific intentions to act? If I intend to become a good tennis player, I will form innumerable specific intentions to practice, study, and compete; if I didn’t I could not be said to have that intention. What reality could there be to the mind that is not manifested in the various activities of the mind? Aren’t mental actions and events the only things in the mind that can be introspected? When I know what I believe don’t I just know the episodic thoughts I am disposed to have? I can’t directly introspect my mental states, only the events that are associated with them. How can I know anything about my memories except by reference to the acts of remembering that manifest them? Introspection is knowledge of what my mind is doing.
Internal behaviorism respects the active nature of mind while avoiding the problems afflicting external behaviorism. External behavior is neither necessary nor sufficient for having a mind (paralysis and robots), but surely mental behavior is necessary and sufficient for having the attributes of mind. How could we disconnect beliefs from dispositions to judge, emotions from dispositions to feel, or personality traits from dispositions to choose? To be mentally paralyzed is to lose one’s mind, and there cannot be a mindless robot endowed with mental activity (but no mental states, traits, faculties, or systems). We are analyzing one part of the mind by reference to another part of the mind, not trying to analyze the mind by moving outside the mental realm altogether. The mind does not reduce to muscular contractions, to be sure, but it might reduce to its own actions—as it were, mental contractions. Of course, internal behaviorism does not make the mind public in the way external behaviorism does; but that was a misguided and quixotic project. Indeed, we might well favor internal behaviorism precisely because it keeps the mind where it should be—resolutely private. The mind consists of inner behavior—hidden, directly known only to the subject, removed from the public world of bodies. The deed is basic, but it is a private deed.
Once we have formulated this kind of inward-looking behaviorism we might venture into more sophisticated versions of the basic idea. Thus we might replace the idea of simple dispositions to mental behavior with something more like functionalism: a mental state is a functional state existing within a web of other mental states and connecting with mental actions and events. If I desire some chocolate and believe there is chocolate in the fridge, I will make the decision to go to the fridge; the belief and desire interlock and lead to the mental action of decision-making. Desires also function holistically in the production of choices, decisions, and intentions, so we will want to build that into our account of how desires relate to mental actions and events. The dispositions to mental behavior will be complex and interdependent; but analytic bedrock will consist of appropriate activities of mind. Thus the spirit of functionalism is maintained while its commitment to bodily behavior is dropped. The mind is a functional system, but the functions are defined over mental inputs and outputs—things like events of perception and actions of judging. We will have no problems of “absent qualia” or “inverted qualia” under such a conception, since the mental is part of the very analysis of the mental. 
There is really nothing oxymoronic about the phrase “internal behaviorism”, just certain dispensable prejudices. Mental acts are as real as physical acts—the realm of action extends into the mind: calculating, talking to oneself, imagining, problem solving, and so on. So there is nothing metaphysically problematic about trying to use mental actions to give a general account of the mind—reducing it all to mental activity. The view may be misguided, but it is not in principle ruled out by the very definition of “behavior”. No doubt classic behaviorists were motivated by anti-mentalist assumptions, but the core of the position is detachable from all that, namely that the mind is best understood in terms of activity. The mental deed is basic—mental doing precedes mental being. We should therefore add internal behaviorism to the list of logically available metaphysical theories of the mind.
 We can either accept reductive internal behaviorism or eliminative internal behaviorism: we analyze everything mental in terms of dispositions to mental behavior or we simply deny that that there is anything to the mind except such behavior. The view suits an idealist attracted by the notion that mental being is a matter of deeds of some sort.