"actum conversationale," -- from Grice's Dictionary

ACTUM. act, f. L. agere, to do. Some philosophers draw a distinction between acts and actions and suggest that while an act is the deed that is done, an action is the doing of it. But most believe that this distinction is hard to maintain and take an act as a synonym for an action. Although there are actions in nature, such as the action of a river on its bank, an action is generally defined as what is intentionally done by a human rational agent. Natural action is described as a mere process, happening, or occurrence. Action has been the focus of much discussion in recent philosophy of mind, especially concerning human intention and deliberation. Many theories have been developed to explain what it means to act intentionally and to show how to distinguish actions from other events involving persons. On one standard account, an action is an event by which an agent brings about changes through bodily movement. A rival mental action theory argues that not all actions involve bodily movement and identifies actions with primary mental events in the causal chain between the agent and behavioral events. According to the causal theory of action developed by Davidson, Searle, and Goodman among others, actions are the effects of primary mental events. Other philosophers reject such primary mental events and deny that actions are events at all. One bodily movement can bring about, directly and indirectly, many changes and the consequences of this for identifying and explaining actions are unclear. X moves his hand; by moving his hand, he turns the steering wheel; and by turning the steering wheel, he drives his car; and so on. Is there one action in this case or are there many? When should we distinguish an action from its consequences? Some philosophers suggest that we can deal with these problems by identifying basic actions that cause other actions but that are not themselves caused by actions. But there is much dispute regarding how to identify basic action. Actions can be discussed in isolation, but they often occur in a pattern of activity either in a single life or involving others. Social action was profoundly explored by Weber. If we seek a causal account of action, are actions caused by reason, desire, or both? Would another framework be more appropriate for explaining or understanding action either within a causal account or as a rival to it? It is unclear whether an explanation by reasons that is not a form of causal explanation is coherent. Answering such questions requires the analysis of many key notions, such as motives, intentions, voluntary and involuntary action, practical reason, wants, and desires. The question of explaining action is closely associated with the problem of free will and determinism and the problem of responsibility. Another much debated problem in philosophy of law and moral philosophy is the relation between action and omission, inaction or negligence. “The word ‘action’ does not very often occur in ordinary speech, and when it does it is usually reserved for fairly portentous occasions. I follow a useful philosophical practice in calling anything an agent does intentionally an action, including intentional omission.” Davidson, Essays on Actions and Events.