An action is an event that an agent performs for a purpose, that is guided by the person's intention. The first question in the philosophy of action is to determine how actions differ from other forms of behavior, like involuntary reflexes. According to Ludwig Wittgenstein, it involves discovering "[w]hat is left over if I subtract the fact that my arm goes up from the fact that I raise my arm". There is broad agreement that the answer to this question has to do with the agent's intentions. So driving a car is an action since the agent intends to do so, but sneezing is a mere behavior since it happens independent of the agent's intention. The dominant theory of the relation between the intention and the behavior is causalism: driving the car is an action because it is caused by the agent's intention to do so. On this view, actions are distinguished from other events by their causal history. Causalist theories include Donald Davidson's account, who defines actions as bodily movements caused by intentions in the right way, and volitionalist theories, according to which volitions or tryings form a core aspect of actions. Non-causalist theories, on the other hand, often see intentions not as the action's cause but as a constituent of it.
An important distinction among actions is between non-basic actions, which are done by doing something else, and basic actions, for which this is not the case. Most philosophical discussions of actions focus on physical actions in the form of bodily movements. But many philosophers consider mental actions to be a distinct type of action that has characteristics quite different from physical actions. Deliberations and decisions are processes that often precede and lead to actions. Actions can be rational or irrational depending on the reason for which they are performed. The problem of responsibility is closely related to the philosophy of actions since we usually hold people responsible for what they do.