Friday, February 17, 2006

Hume's Fork

Spur writes here

Leibniz and Hume have the same basic distinction in mind, between those truths which are necessary and can be known a priori, and those which are contingent and can only be known a posteriori. The two philosophers use slightly different terminology, and Leibniz would balk at Hume's use of 'relations between ideas' in connection with truths of reason only, but the basic distinction seems to me to be the same.

But the question is more difficult, and is related to a change in logic that happened at the very beginning of the early modern era. The scholastic logicians said that in a proposition (which for them meant a sentence) the predicate is affirmed or denied of the subject. 'Subject' and 'predicate' here are objectively existing things.

Influenced by Descartes, Antoine Arnauld argued that it is not one THING that is predicated of another thing, but one IDEA that is predicated of another idea. Locke (who studied Arnauld's logic carefully) introduced this to the English world (Book IV of the essay is the locus classicus). For example, he sets its down as a principle, that all our knowledge consists in perceiving certain agreements and disagreements between our ideas.

There you have Hume's fork. Before, there was the difference between accidental and essential propositions. An essential proposition is where the predicate belongs in the subject by right, as it were. An accidental proposition is whether the predicate belongs in the subject, but possibly may not. It is not relevant whether this can be known or not. There are (as Aquinas notes) essential propositions which cannot be known because mere humans cannot understand the true meaning of the word which signifies the subject. But the notion of a proposition true in itself but unknowable because the 'subject' is unknowable, is impossible where the proposition consists of ideas stuck together.

In summary: Hume's fork is a consequence of the early modern view of the proposition. The scholastic view was that the proposition connects things. The early modern view is that it connects ideas. The distinction between truths of reason and truths of fact only makes sense on the latter view.

There a number of passages which support this argument & I will make a posting in due course.


Martin Cothran said...

You say that "The scholastic logicians said that in a proposition (which for them meant a sentence) the predicate is affirmed or denied of the subject. 'Subject' and 'predicate' here are objectively existing things." And you attribute the view that the subject and predicate represent "ideas" to the influence of Descartes.

My understanding of scholastic (or "Aristotelian") logic is that it is the "science of second intentions", and that it purports to deal with relationships between beings of reason, not empirical facts, although the relationship between the beings of reason is not unimportant. And, in fact, that the whole reason that five of the 19 recognized valid syllogism forms have been rejected by modern logicians is precisely because THEY see the terms in categorical syllogisms as necessarily referring to real, rather than logical, entities, in accordance with their nominalist assumptions. I'm referring to the debate over existential import here, of course.

Interesting post, but help me out here.

Edward Ockham said...

There's a long and short answer to this. The short answer is the standard position (as expressed by Mill, e.g., and by Kneales in their history of logic, see e.g. p. 197) that 'man is a universal and Callias is an individual' is expressing the difference between two kinds of things (not words, or ideas).

The long answer (short version of) is that there was argument about this in medieval times just as now, and that the medieval writers were not so oblivious to the use-mention distinction as the standard account would have.

On existential import, correct. I wrote something about this here

and will be presenting a paper on a connected subject at the Square of Opposition conference at Montreux in July.

Forgive my curiousity, but I Googled 'Martin Cothran' who appears to be doing some interesting work with Latin and traditional logic. Would that be you? Then we are allies of a sort. We have just decided to send our son to a similar school in England.

With best wishes.