I have always thought the main argument for/consequence of Hume's law is that just because something is in a certain way, that is not an argument for it to remain that way. E.g., just because homosexual acts were forbidden in most Western countries before the 20th century that is not an argument it should remain so.

Instead, if you want homosexuality to remain outlawed you must produce a moral argument why consenting adults shouldn't be allowed to do whatever they like with their bodies.

But when I read the Wikipedia-article about Hume's law, except for 1-2 sentence(s) in the introductory paragraph, all other examples is quite, or very, different from my understanding of it.

Have I misunderstood something? What is the main point/consequence of Hume's law?

  • Others will respond with a better grasp of this, but his Law originates in his observation that human perception of the 'sensible' world occurs only in the present moment. This means that we do not actively participate in any type of continuum which would allow us to make verifiable judgements. We do not experience the past or the future in real-time. So in terms of moral judgements, these can only ever remain at the speculative level. CMS
    – user37981
    Feb 23, 2020 at 14:02
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    If by "Hume's law" you mean the is-ought guillotine then it is indeed nothing like what you describe. It concerns the impossibility of deriving values or norms from facts, ought from is, however things might be in the world does not decide how we should act. Yours seems to be a peculiar amalgamation of this with Hume's also deflation of causality: there is no law or reason why the same causes being followed by the same effects in the past should continue to do so in the future. But that concerns natural events, not human norms and values
    – Conifold
    Feb 24, 2020 at 4:50
  • @Conifold "It concerns the impossibility of deriving values or norms from facts" - isn't that exactly what I describe? The law is a fact but that doesn't make it morally right or justifiable, that is - a description how things ought to be.
    – d-b
    Feb 24, 2020 at 7:03
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    The "facts" meant are facts of nature describing the state of the universe, not norms maintained by society by law or tradition. Hume's point is that, in a sense, "morally right" is not justifiable at all. The most we can do is derive more specific norms/values from more general ones, but at the root of it there is always a choice that the state of the universe has nothing to do with (although it may influence specific choices made in pursuit of the root one).
    – Conifold
    Feb 24, 2020 at 7:15
  • I haven't heard a good argument for Hume's law and don;t believe it is a law. But perhaps this is not relevant.
    – user20253
    Mar 6, 2020 at 11:33

1 Answer 1


Hume's Law has been taken to be at least one of the following:

(i) an ought judgement is deducible only from an evaluative judgement;

(ii) an ought judgement is deducible only from a prescriptive judgement;

(iii) an ought judgement is deducible only from another ought judgement;

(iv) an ought judgement is not deducible from a factual judgement

(G. R. Grice, 'Hume's Law', Proceedings of the Aristotelian Society, Supplementary Volumes, Vol. 44 (1970) 89-103: 90.

An example of an evaluative judgement would be, 'It is in A's best interests to do X'. A prescriptive judgement takes the different form, 'A ought to do X'.

'Hume's Law' is generally taken in sense (iv) and to hold that moral claims cannot be inferred from exclusively non-moral claims. This assumes, of course, that moral claim are not factual; Hume deals with this point (whether satisfactorily or not) in Treatise III.I.1 (Selby-Bigge, re. Nidditch: Oxford, 1978: 468-9).

You have not misunderstood Hume at all. According to Hume's Law it logically does not and cannot follow from the fact that homosexuality was forbidden in most Western countries before the twentieth-century that it ought to be forbidden now. From 'it is the case that it was forbidden' we cannot deduce that 'it ought to be forbidden'.

  • Thank you for your answer. So the Wikipedia article is unclear or less then perfectly worded? Or are there more nuances to HL?
    – d-b
    Mar 3, 2020 at 21:33
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    Wiki is generally an excellent aid but I don't think it's strongest on detailed philosophy. If you want an online guide for philosophy, the Stanford Encyclopaedia of Philosophy is hard to beat. Best - Geoffrey
    – Geoffrey Thomas
    Mar 4, 2020 at 8:54
  • Can you suggest an article in SEP I should about this? Made a search but drowned in results...
    – d-b
    Mar 4, 2020 at 17:23
  • See plato.stanford.edu/entries/hume-moral - §5.
    – Geoffrey Thomas
    Mar 4, 2020 at 17:33

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