Theory of Action is an area in philosophy concerned with theories about the processes causing willful human bodily movements of a more or less complex kind. This area of thought involves epistemology, ethics, metaphysics, jurisprudence, and philosophy of mind, and has attracted the strong interest of philosophers ever since Aristotle's Nicomachean Ethics (Third Book). With the advent of psychology and later neuroscience, many theories of action are now subject to empirical testing.
Basic action theory typically describes action as behavior caused by an agent in a particular situation. The agent's desires and beliefs (e.g. my wanting a glass of water and believing the clear liquid in the cup in front of me is water) lead to bodily behavior (e.g. reaching over for the glass). In the simple theory (see Donald Davidson), the desire and belief jointly cause the action. Michael Bratman has raised problems for such a view and argued that we should take the concept of intention as basic and not analyzable into beliefs and desires.
In some theories a desire plus a belief about the means of satisfying that desire are always what is behind an action. Agents aim, in acting, to maximize the satisfaction of their desires. Such a theory of prospective rationality underlies much of economics and other social sciences within the more sophisticated framework of Rational Choice. However, many theories of action argue that rationality extends far beyond calculating the best means to achieve one's ends. For instance, a belief that I ought to do X, in some theories, can directly cause me to do X without my having to want to do X (i.e. have a desire to do X). Rationality, in such theories, also involves responding correctly to the reasons an agent perceives, not just acting on wants.
While action theorists generally employ the language of causality in their theories of what the nature of action is, the issue of what causal determination comes to has been central to controversies about the nature of free will.
Conceptual discussions also revolve around a precise definition of action in philosophy. Scholars may disagree on which bodily movements fall under this category, e.g. whether thinking should be analysed as action, and how complex actions involving several steps to be taken and diverse intended consequences are to be summarised or decomposed.
For example, throwing a ball is an instance of action; it involves an intention, a goal, and a bodily movement guided by the agent. On the other hand, catching a cold is not considered an action because it is something which happens to a person, not something done by one. Generally an agent doesn't intend to catch a cold or engage in bodily movement to do so (though we might be able to conceive of such a case). Other events are less clearly defined as actions or not. For instance, distractedly drumming ones fingers on the table seems to fall somewhere in the middle. Deciding to do something might be considered a mental action by some. However, others[who?] think it is not an action unless the decision is carried out. Unsuccessfully trying to do something might also not be considered an action for similar reasons (for e.g. lack of bodily movement). It is contentious whether believing, intending, and thinking are actions since they are mental events.
Some would prefer to define actions as requiring bodily movement (see behaviorism). The side effects of actions are considered by some to be part of the action; in an example from Anscombe's manuscript Intention, pumping water can also be an instance of poisoning the inhabitants. This introduces a moral dimension to the discussion (see also Moral agency). If the poisoned water resulted in a death, that death might be considered part of the action of the agent that pumped the water. Whether a side effect is considered part of an action is especially unclear in cases in which the agent isn't aware of the possible side effects. For example, an agent that accidentally cures a person by administering a poison with which he was intending to kill him.
A primary concern of the philosophy of action is to analyze the nature of actions and distinguish them from similar phenomena. Other concerns include individuating actions, explaining the relationship between actions and their effects, explaining how an action is related to the beliefs and desires which cause and/or justify it (see practical reason), as well as examining the nature of agency. A primary concern is the nature of free will and whether actions are determined by the mental states that precede them (see determinism). Some philosophers (e.g. Donald Davidson) have argued that the mental states the agent invokes as justifying his action are physical states that cause the action. Problems have been raised for this view because the mental states seem to be reduced to mere physical causes. Their mental properties don't seem to be doing any work. If the reasons an agent cites as justifying his action, however, are not the cause of the action, they must explain the action in some other way or be causally impotent.
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