I am on the hunt for a deductive argument that is valid in point of logical form and that takes us from a premise set all of whose members are purely factual to a categorically (as opposed to hypothetically or conditionally) normative conclusion. Tully ( = Cicero?) the Commenter offered an argument that I make explicit as follows:

1. It is snowing

2. For any proposition p, if p, then it is true that p.

Therefore

3. If it is snowing, then it is true that it is snowing. (2, UI)

Therefore

4. It is true that it is snowing. (1, 3 MP)

5. For any p, if p is true, then one ought to believe that p.

Therefore

6. If it is true that it is snowing, then one ought to believe that it is snowing. (5, UI)

Therefore

7. One ought to believe that it is snowing. (4, 6 MP)

Does this argument do the trick? Well, it is plainly valid. I rigged it that way! Is the conclusion categorically normative? Yes indeed. Are all of the premises purely factual? Here is the rub. (5) is a normative proposition. And so the argument begs the question at line (5). Indeed, if one antecedently accepts (5), one can spare oneself the rest of the pedantic rigmarole.

But I have a second objection. Even if the move from 'is' to 'ought' internal to (5) is logically kosher, (5) is false. (5) says that whatever is true is such that one ought to believe it. But surely no finite agent stands under an obligation to believe every true proposition. There are just too many of them.

If one ought to do X, then (i) it is possible that one do X, and (ii) one is free both to do X and to refrain from doing X. But it is not possible that I believe or accept every true proposition. Therefore, it is not the case that I (or anyone) ought to believe every true proposition. (One can of course question whether believings are voluntary doings under the control of the will, and (surprise!) one can question that questioning. See my Against William Alston Against Doxastic Voluntarism.)

Still and all, truth does seem to be a normative notion. (5) doesn't capture the notion. What about:

5*. For any p, if p is true, then p ought to be believed by anyone who considers it.

The idea here is that, whether or not there are any finite minds on the scene, every true proposition qua true has the intrinsic deontic property of being such that it ought to be believed. I say 'intrinsic' because true propositions have the deontic property in question whether or not they stand in relation to actual finite minds.

But of course plugging (5*) into the above argument does not diminish the argument's circularity.

Here is a possible view, and it may be what Tully is getting at. Truth is* indissolubly* both factual and normative. To say of a proposition that it is true is to describe how it stands in relation to reality: it represents a chunk of reality as it is. But it is also to say that the proposition qua true functions as a norm relative to our belief states. The truth is something we ought to pursue. It is something we ought doxastically to align ourselves with.

This is murky, but if something like this is the case, then one can validly move from

p is true

to

p ought to be believed by anyone who considers it.

The move, however, would not be from a purely factual premise to a categorically normative conclusion. My demand for a valid instance of such a move might be rejected as an impossible demand. I might be told that there are no purely factual premises and that if,* per impossible*, there were some, then *of course* nothing normative could be extracted from them.

What say you, Tully?

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