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First, to quote Hume:

In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprised to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is, however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, it's necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.

My original belief about what Hume was saying, here, is that there is a syntactic gap between predicative terms and deontic terms. The trivial counterexample, though, is, "There is an obligation (or I am obligated) to do X; therefore, X ought to be done (by me)." (Waive, for a moment, the distinction such as is drawn by John Rawls between obligations and duties.) Moreover, one might think that disjunction is syntactically distinct from, say, conditionals, or existential from universal quantification, yet there are conversions available modulo semantics that explain how we infer an IF from an OR (or an OR from an IF), etc. and perhaps that is how one might infer an "ought" from an "is."EDIT

So my other interpretation was: Hume's argument is a syntax-emphasized example of what the "naturalistic" fallacy is a semantics-emphasized example. One's feeling for this "fallacy" will influence one's desire to link Hume and Moore as nodes in a clearly evolving history of moral philosophy, perhaps.

However, I was going through Kant's first Critique again, and I got caught on this passage:

For as regards nature, experience presents us with rules and is the source of truth, but in relation to ethical laws experience is the parent of illusion, and it is in the highest degree reprehensible to limit or to deduce the laws which dictate what I ought to do, from what is done.

I don't remember for sure whether he actually did say the following, but even if Kant left this topic at just the above passage, he could have explained the quoted sentence like this:

  1. Many people doing something, or having a hard time not doing something else, does not mean that the things done or not done ought to be or not be done. A popular behavior is not moral because it is popular, and a tempting choice is not moral for being an oft-fallen-for temptation.
  2. More importantly, successfully achieving something complex/difficult is not to be taken as proving divine or equivalent favor in one's endeavors. The "is" of achieving something is not identical to the "ought" of what we are to set out looking to achieve in the first place.

Did Kant say as much elsewhere? Or did he not say anything that would make (1) and (2) insufficient for understanding what he says in the first-Critique passage that was quoted?


EDITSimilarly, is there a logical (syntactic/grammatical) gap between is and would, or is and could, though? So the syntactic interpretation of the problem still seems weaker than the semantic one (FOL sentences at least naturally carry over directly into standard modal propositional logic; there is of course no apparent deontic carryover so automated; even an axiom to such an effect would render the relation less direct).

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    I think you have two different questions in the title and in the body. Did Kant read the is-ought problem in a "normal" way, as epistemological irreducibility of norms to facts? Yes, he did, in fact, his is-ought guillotine is even sharper than Hume's, see Osmola, "Is" and "Ought" in Hume's and Kant's philosophy. Did he also have a moral qualm with people sinking their aspirations to the level of "what is done", as "reprehensible" suggests? Sure. He coached it in terms of rationality rather than divinity or temptations, but that is separate.
    – Conifold
    Jan 5, 2023 at 0:45
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    @Conifold, I would also have to integrate Kant's claim that, "I ought to," means, "I would, if reason alone determined my actions." He seems to indicate that he is describing practical reason, yet somehow from a description of this "faculty" there follows the categorical imperative prescriptively. He says something like this when he says that the fact of reason announces itself, "sic volo, sic jubeo." Jan 5, 2023 at 1:21
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    That is because Kant does not treat reason the modern way, as a detached describer, his one and the same reason has both theoretical and practical function. And this is his solution to the guillotine: while is and ought are two separate spheres, the same reason functions in both, his rationality is jointly descriptive and normative. So Kant is not deriving the categorical imperative from descriptions of practical reason, he rather conveys what the latter dictates, see e.g. Kelsen, Is and Ought in Kant's Philosophy.
    – Conifold
    Jan 5, 2023 at 6:31
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    "No duality of Is and Ought can be found in Kant's philosophy for the very simple reason that, for Kant, the moral norm (the moral Ought, the moral law) emanates from reason in its function as practical reason, the very same reason whose function it is to know what is. For Kant says explicitly in the Foundations of the Metaphysics of Morals that practical reason, the moral legislator, is fundamentally the same as theoretical reason... 'because in the final analysis there can be but one and the same reason which must be differentiated only in application'".
    – Conifold
    Jan 5, 2023 at 6:33
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    The notions of ought/ought not are predicated on goals/objectives/aims. If I know (is) x causes y and my aim is to cause y, I should (ought) to do x. Jan 5, 2023 at 11:03

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