Are Reasons Causes?
It used to be held in the 1950s that reasons are not causes (the “logical connection” argument), but the tide turned in the 1960s. The new orthodoxy was that rational explanation of actions is a species of causal explanation: beliefs and desires are the causes of action. True, this is a special kind of causal explanation, since reasons have a rational structure exhibiting logical connections; but that is no bar to their also being causes (efficient causes, in Aristotle’s terminology). Beliefs and desires cause actions in the same sense that impacts cause motions or smoking causes cancer. Since a reason is a combination of a belief and a desire it too causes actions: it causes what it rationalizes. I go to the shops intending to buy fruit, desiring some fruit and believing that the shops are the place to go; these mental states cause my shop-going behavior. It is rational to go to the shops if you desire fruit and you believe the shops are the place to get it, and these attitudes operate causally to bring about the behavior in question. The attitudes are causal factors, triggering events, effect-producers; no doubt they are underlain by brain causes that exploit efferent nerves and send neural volleys. What we have here is just another example of multi-factor common-or-garden causation.
But another point about reasons and actions also gained traction at around this time, namely that desires and beliefs cannot act on their own—they must always work as a couple. Suppose I leave the house with an umbrella: you might surmise that I do so because I believe it is about to rain. But that is only a rational action if I also desire to keep dry: I might have that belief and fancy a dousing, so I leave the umbrella at home. Similarly, a desire to stay dry will only lead me to carry an umbrella if I believe umbrellas are a good way to keep dry. The desire supplies an end, but it takes an instrumental belief to determine a particular type of action. The action is a means to satisfying a desire, but it takes a belief to link the desire to a suitable action. This is a kind of confined holism whereby beliefs and desires only cause actions by conjoining with each other. The point I want to emphasize is that the components of reasons (beliefs and desires) have no intrinsic causal power with respect to action. Logically they cannot bring about actions individually but must rely on each other to generate an action. It is not that they have no specific causal powers considered singly; rather, they cannot cause action in isolation. If you ask what action a desire to keep dry will cause, you will get no answer, because that depends on what the agent believes; and similarly for the belief that umbrellas keep you dry. It is only as a pair that a specific action emerges as the rational thing to do: if you want this and you believe that, then (and only then) will an action of a certain type ensue. Actions are selected according to means-end reasoning, and that requires the belief-desire combination. Desires can cause both mental and physical happenings, as when one desire causes another desire or induces a flight of imagination, or when the desire causes the body to react in a certain way (blushing, etc.); but in the case of action only the pair together can produce anything. But then, isn’t there a problem about the causal story, since the components of reasons lack determinate causal powers with respect to action? Normally when two causal factors are at work we have a causal contribution stemming from each, as when two people combine to lift a heavy object: but nothing like this holds of beliefs and desires—considered separately there is no causal input into the motor system. So even if reasons cause actions their components don’t operate in the standard causal manner: there is no cumulative or additive causal contribution. Each is impotent in relation to action, so how can they combine to produce a causal result? We would have a strange kind of causal holism unlike anything else in nature: causation by the whole resulting from non-causation in the parts. Wouldn’t it be better to abandon the idea of rational explanation as causal explanation?
And then there is this familiar point: the holism is also operative across reasons. For an agent will not act on a given reason unless his other reasons are conducive: I might want to keep dry and believe an umbrella will do the trick, but I might also reason that it’s too much trouble to carry an umbrella or that I will look uncool with one or that it’s against my religion to ward off God-given showers. So reasons only cause actions (if they do) against the background of other reasons, but nothing like this holds outside of the rational realm. The causal story thus seems inconsistent with a commonsense form of holism: the alleged causes just don’t operate in the way causes are generally wont to do. The causation is not atomistic (bottom-up) in the standard style–but then why speak of causation at all? The model of specific causal powers possessed by separate states or events breaks down. The causal thesis conflicts with the two kinds of holism described (and generally accepted). There is no causal line linking beliefs and desires separately to specific types of action, so why speak of causality at the level of combinations of the two?
Let me emphasize that this point arises from the logical nature of reasons: the desire component and the belief component are logically incapable of producing a specific action individually. The desire needs an instrumental belief to generate a means, while the belief has no practical consequences without an accompanying desire. Action cannot logically spring from either component alone, but then the model of additive causation breaks down. This is nothing like a combination of separate forces leading to a certain effect. A being without desires will logically never act, and a being with only desires will be bereft of a means of satisfying the desires it has. When we give the reason for which an agent acted we don’t specify two causal factors that combined to produce that action, since neither belief nor desire can cause actions by themselves, or even tend to produce specific actions. This is nothing like explaining why someone has food poisoning by saying that she ate both bad oysters and off chicken. If reasons cause actions, they do so by some magical process that generates holistic causation from atomistic non-causation. Whatever causal powers are possessed by beliefs and desires separately are not exploited in the production of rational action; so it seems merely verbal to insist that causation is operating here as it operates elsewhere. We can call this causation—the concept is capacious—but it is not the kind of causation with which we are familiar in paradigm cases of efficient causation. Certainly it would be futile to seek laws connecting desires with actions or beliefs with actions, as if these could be separate things.
The holism of belief and desire was initially used to refute behaviorism, since no behavioral disposition is associated with a given desire independently of belief (and contrariwise). But the same point undermines the idea that belief and desire operate as summative causal factors in the production of action: no unique disposition to action can be associated with a given belief or desire that might combine with another such disposition. This is a special feature of practical reasoning as means-end reasoning. The type of reasoning that is involved precludes the model of separable causal powers joining forces, because ends need means and means need ends in order to lead to rational action. No causation without causal separation. It is the logic of practical reasoning that precludes the standard model of causal explanation. They were onto something in the 1950s, even though they might have misrepresented what it was.
 I hope it is clear that I am not denying that in certain cases beliefs can motivate, as in cognitivist theories of moral motivation. By “desire” I mean (as is standard) any kind of pro-attitude, even if it takes the form of a value judgment; it will still need an instrumental belief to lead to concrete action.