Belief, Desire, and Action



Beliefs, Desires, and Actions


Consider actions in which the agent uses a piece of technology (in a broad sense) to achieve a desired goal: using a car to get to a certain place, using a cell phone to communicate, taking an umbrella out in the rain, using a hammer to knock in a nail. It is natural to analyze the psychological background of such actions as involving (a) a certain desire and (b) a belief about the means to achieving that desire. For instance, the agent wants to get to a certain place and believes that driving a car is the best means to achieve this goal. There is a combination of belief and desire at work, which leads to the performance of the action. Theorists of action have seen in this kind of case a general analysis of action: any action is caused and explained by the presence of an antecedent pair of a desire and a belief, where the belief specifies the means to be adopted to satisfy the desire. The desire alone will not prompt or predict the specific action performed—an accompanying belief is also required; nor will the belief alone suffice to elicit the action—an accompanying desire is required. A desire to stay dry will not prompt you to take an umbrella unless you believe that umbrellas keep you dry, and the belief that umbrellas keep you dry will not prompt you to take one unless you desire to stay dry (you might feel like getting soaked today). Thus there arises a certain doctrine about the psychological basis of action: any action requires the presence of a desire anda belief—both are necessary conditions (and together possibly sufficient) for an action to occur. This is supposed to be an interesting and unique fact about action and its explanation, suggesting a certain kind of “holism” about psychological explanation. Let’s call it the “Combination Thesis” (or “CT” for short): the thesis that all actions are consequences of a belief-desire pair acting in concert. Thus we arrive at something called “belief-desire psychology”, taken to be a general format for psychological explanation: any explanation of action requires the specification of a desire and an instrumental belief concerning how best to satisfy that desire. Action is the result of something cognitive and something appetitive operating together.

I propose to question this widely held picture. I think it arises from overgeneralizing one sort of example of action—the kind that involves means-end reasoning. In particular, I think that some actions occur without any instrumental belief and some occur without any desire (in a natural sense of “desire”). That is, there are one-factoractions—just a belief or a desire operating on its own. The Combination Thesis is false, except in a limited range of cases; it is not fundamental to action as such. Let us consider a very simple kind of action: flexing one’s index finger. Suppose an agent has a desire to flex his index finger and does so: what means-end belief accompanies this action? On the face of it, none: he didn’t believe that a certain device was a good means to bring about the desired result. The agent didn’t think that contracting certain muscles in his forearm would be a good means to flex his finger—he simply did it. And even if such a thought had entered his head (maybe he specializes in hand physiology), there would be the question of whether thataction needed a belief about means for it to be performed (say, initiating efferent nerve impulses from the brain). No, the action simply resulted from a desire, with no means-end belief involved (no technology is being exploited). It is the same for swallowing, breathing, walking, swimming, etc. You don’t believe that swallowing is a good way to get food into your stomach when you eat, or that putting one foot in front of the other is a good way to walk—any more than animals do. You just do it. It is absurdly intellectualist to suppose otherwise. It is not as if you have an array of options available for getting food inside you, such as inserting it through your navel, and you choose one of them as the best means in the circumstances. Chewing and swallowing are just nature’s way of getting fed, not a cunning plan you have devised for achieving satiation.[1]You have a desire for food, so you do what comes naturally, as you do when inhaling oxygen into your lungs. In general, movements of the body (often called “basic actions”) are not preceded by means-end reasoning: a person never moves her body by reasoning about the best means of doing so. That is, basic actions are not subject to CT. Raising my arm is not something I need an instrumental belief to perform. If I want to raise it, I raise it, without consulting possible means. Thus the explanation of a basic action has the form, “Xdid Abecause he desired to do A”. It is the same for adult humans, infant humans, and most animals: basic movement is caused by a desire not by a desire-belief combination. There is simply no need for belief: the mind and body are just wired (innately or by learning) to translate desire into action. The right thing to say is that where there is means-end reasoning there is a belief corresponding to the means that combines with a desire, but in more basic cases there is no such belief, since there are no such means. A specific feature one kind of action has been overgeneralized to apply to all action. Indeed, whenever CT does hold there is always a basic action for which it does not hold, i.e. a movement of the body. This is even clearer for purely mental action such as calculating in the head: if I add two numbers in my head, I don’t have an instrumental belief about how best to get the result I want. I want the answer and I’m wired to get it (I know arithmetic); I don’t need any superintending belief about the best means of getting it. Another way to put the point: in tactical practical reasoning agents have instrumental beliefs, but most action is not of a tactical kind. What psychologists call sensory-motor activity is generally not tactical or instrumental or belief-driven; it is automatic, programmed, not thought out.

But is desire always necessary for action? It depends what you mean by “desire”, which tends to be a philosopher’s term of art (sometimes glossed as “pro-attitude”). It seems right to say that the agent needs to view the action favorably (certainly not unfavorably), but there are ways of doing that that are not really cases of desire. Suppose you believe that you have a certain desire but you don’t really have it (you have been brainwashed into the belief): won’t you still be inclined to do the thing in question? Then your action will be motivated by a belief abouta desire, but not by that desire—you apply to medical school, say, because you have been brought up to believe that medicine is your calling (in fact, it’s opera). This would be a case in which you act on a belief without the corresponding desire, though you can be said to view the action favorably. And isn’t it generally true that desires influence actions only if they are recognizedin some way? How could desires of which you are completely ignorant figure as causes of action (even unconscious desires need to be recognized by the unconscious executor)? Their existence has to be registered or acknowledged. So something like belief has to be added to them to produce action; and then we have the question how much the belief contributes to motivational force. This gets pretty messy, psychologically. The neat picture of the pristine desire and its helpful belief companion starts to seem too simplistic. Motivation has (or can have) a more complex and variable structure.  You can do something simply because you have a sudden urge to do it, and you can also do something because you believe you desire to (though you don’t)—in either case you lack one of the components postulated by CT. So there are now three types of case to consider: (i) belief and desire in combination, (ii) desire alone, and (iii) belief alone. Some theorists have argued that moral motivation consists of nothing but a moral belief; we need not take a stand on that issue to accept that beliefs aboutdesire can play a motivational role. Being under the impression that you have a certain desire can act as a prompt to action, whether you have that desire or not. Maybe the only general thing we can say is that the action has to look desirable to you—there is something to be said in favor of doing it. This can take the form either of desire plus belief, or simply desire, or believed desire (or maybe just belief that the action would be morally good). Animal action will largely consist of the second category; agents with advanced practical reasoning will do a good deal of the first kind; the third kind will be restricted to those individuals deluded or confused about what it is they really want. There is no psychological structure common to all cases. The psychology of action is not monolithic.

Suppose someone suggests that action is what is caused by need, so that to explain an action we must specify what need it serves. This theorist is perhaps impressed by the actions of certain animal species of a somewhat primitive type. The natural response would be that this is too simple, too parochial: not every action is prompted by a biological need, and actions sometimes require practical reasoning involving instrumental belief. The need theory applies to some cases but certainly not to all. Well, belief-desire psychology, as currently understood, is rather like that: it fits some cases well enough, but it is too uniform and simple. There are a variety of different kinds of motivational state, ranging across a wide spectrum. In some ways the theory is too complex (because of basic actions) while in others it is not complex enough (because of cases like false beliefs about one’s desires). Thus reasons for action are of different types, not always resolving into the two-factor model of CT. Pluralism about reasons is the indicated position.[2]


Colin McGinn

[1]Sub-intentional actions, such as rolling one’s tongue around one’s mouth or tapping one’s foot nervously, seem particularly unsuitable to the belief-desire treatment: what instrumental belief do I have when my tongue is rolling around pointlessly? Just as the heart has no instrumental belief when performing the act of pumping blood, so many of our more automatic actions are free of cognitive supervision.

[2]All reasons may be causes, but the causes can vary as to type. Desires themselves can come in many types, from the moral to the animalistic. Nor is there less variety in the concept of belief. It is variety all the way down.

2 replies
  1. Giulio Katis
    Giulio Katis says:

    There are also impulsive actions which seem to require neither beliefs nor desires. Eg a physical outburst due to frustration, or laughing.

    And what about the actions (and inactions) of Hamlet?

    There is the question of whether in a given situation a belief or desire (or any other factor, such as conditioning) is really causing the action vs shaping it. I guess it is one thing to explain variation in actions (why she did X rather than Y), and another to explain the very basis for action (why she did something at all).


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