Hume was an influential eighteenth century Scottish philosopher well known for his empirical approach, which he applied to various fields in philosophy.
It restricts the sphere of practical reason to instrumental rationality concerning which means to employ to achieve a given end.
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.
But many philosophers within the Humean tradition have gone beyond these methodological restrictions and have drawn various metaphysical conclusions from Hume's ideas.
Matters of fact, on the other hand, concern contingent propositions about the world knowable only a posteriori through perception and memory.
[1][5] 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.
This leads to Hume's skeptical conclusion: that, strictly speaking, we do not know that a causal relation was involved.
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.
[7] Jessica Wilson provides the following contemporary formulation: "[t]here are no metaphysically necessary connections between wholly distinct, intrinsically typed, entities".
David Lewis follows this line of thought in formulating his principle of recombination: "anything can coexist with anything else, at least provided they occupy distinct spatiotemporal positions.
[13] Combined with the assumption that reality consists on the most fundamental level of nothing but a spatio-temporal distribution of local natural properties, this thesis is known as "Humean supervenience".
[14][15] An even wider application is to use Hume's dictum as the foundational principle determining which propositions or worlds are possible and which are impossible based on the notion of recombination.
[16][17] Not all interpreters agree that the reductive metaphysical outlook on causation of the Humean tradition presented in the last paragraphs actually reflects Hume's own position.
One important feature of actions, which sets them apart from mere behavior, is that they are intentional or guided "under an idea".
[20][21] On this issue, Hume's analysis of action emphasizes the role of psychological faculties and states, like reasoning, sensation, memory, and passion.
So the movement of the finger flipping the switch is part of the action as well as the electrons moving through the wire and the light bulb turning on.
[21] One important objection to Davidson's and similar Humean theories focuses on the central role assigned to causation in defining action as bodily behavior caused by intention.
[30] Davidson addresses this issue by excluding cases of wayward causation from his account since they are not examples of intentional behavior in the strict sense.
[20] In contemporary philosophy, Hume's theory of practical reason is often understood in terms of norms of rationality.
[43] This can be combined with the thesis that practical reason has something to say about which ends we should follow, for example, by having an impact either on these other states or on desires directly.
[20] A common dispute between Humeans and Anti-Humeans in the field of practical reason concerns the status of morality.
This poses the following threat: it may lead to cases where an agent simply justifies his immoral actions by pointing out that he had no desire to be moral.
It is guided by the idea that there is an important difference between is-statements, which concern facts about the natural world, and ought-statements, which are moral or evaluative claims about what should be done or what has value.
[45][46][47][48] This is important, according to Hume, because this type of mistaken inference has been a frequent source of error in the history of philosophy.
[51] Emotivists, on the other hand, hold that ought-statements merely express the speaker's emotional attitudes in the form of approval or disapproval.
It is reflected on the metaphysical level as the dispute about whether normative facts about what should be the case are part of reality, as realists claim, or not, as anti-realists contend.
[58] He denies the traditional conception, usually associated with René Descartes, that the mind is constituted by a substance or an immaterial soul that acts as the bearer of all its mental states.
Hume's particular version of this approach is usually rejected, but there are various other proposals on how to solve this problem compatible with the bundle theory.