Humeanism refers to the philosophy of David Hume and to the tradition of thought inspired by him. Hume was an influential Scottish philosopher well known for his empirical approach, which he applied to various fields in philosophy. In the philosophy of science, he is notable for developing the regularity theory of causation, which in its strongest form states that causation is nothing but constant conjunction of certain types of events without any underlying forces responsible for this regularity of conjunction. This is closely connected to his metaphysical thesis that there are no necessary connections between distinct entities. The Humean theory of action defines actions as bodily behavior caused by mental states and processes without the need to refer to an agent responsible for this. The slogan of Hume's theory of practical reason is that "reason is...the slave of the passions". It restricts the sphere of practical reason to instrumental rationality concerning which means to employ to achieve a given end. But it denies reason a direct role regarding which ends to follow. Central to Hume's position in metaethics is the is-ought distinction. It states that is-statements, which concern facts about the natural world, do not imply ought-statements, which are moral or evaluative claims about what should be done or what has value. In philosophy of mind, Hume is well known for his development of the bundle theory of the self. It states that the self is to be understood as a bundle of mental states and not as a substance acting as the bearer of these states, as is the traditional conception. Many of these positions were initially motivated by Hume's empirical outlook. It emphasizes the need to ground one's theories in experience and faults opposing theories for failing to do so. But many philosophers within the Humean tradition have gone beyond these methodological restrictions and have drawn various metaphysical conclusions from Hume's ideas.
Causality and necessity
Causality is usually understood as a relation between two events where the earlier event is responsible for bringing about or necessitating the later event. Hume's account of causality has been influential. His first question is how to categorize causal relations. On his view, they belong either to relations of ideas or matters of fact. This distinction is referred to as Hume's fork. Relations of ideas involve necessary connections that are knowable a priori independently of experience. Matters of fact, on the other hand, concern contingent propositions about the world knowable only a posteriori through perception and memory. Causal relations fall under the category of matters of facts, according to Hume, since it is conceivable that they do not obtain, which would not be the case if they were necessary. For Hume's empiricist outlook, this means that causal relations should be studied by attending to sensory experience. The problem with this is that the causal relation itself is never given directly in perception. Through visual perception, for example, we can know that a stone was first thrown in the direction of a window and that subsequently, the window broke, but we do not directly see that the throwing caused the breaking. This leads to Hume's skeptical conclusion: that, strictly speaking, we do not know that a causal relation was involved. Instead, we just assume it based on earlier experiences that had very similar chains of events as their contents. This results in a habit of expecting the later event given the impression of the earlier one. On the metaphysical level, this conclusion has often been interpreted as the thesis that causation is nothing but constant conjunction of certain types of events. This is sometimes termed the "simple regularity theory of causation".