Tuesday, June 29, 2021

Dr. Smith ate a banana

Suppose you receive this trustworthy report:

  1. Dr. Smith ate a banana.

You are now in a position to learn this additional fact:

  1. Someone whose last name is “Smith” ate a banana.

But (2) does not logically follow from (1). So how do we learn (2) from the report?

Knowledge of English tells us that “Dr. Smith ate a banana” has “Dr. Smith” as the subject and that this sentence attributes eating a banana to the subject of the sentence. Assuming defeasibly that the the use of English in the report is correct, we conclude that someone correctly styled “Dr. Smith” was reported to have eaten a banana. And assuming defeasibly that the report itself is factually correct, we conclude that:

  1. Someone correctly styled “Dr. Smith” ate a banana.

Knowing English, we also know that anyone correctly styled “Dr. Smith” has the last name “Smith”, so we get (2). We also know that anyone correctly styled “Dr. Smith” has a doctorate, so:

  1. Someone with a doctorate ate a banana.

These are instances of the familiar fact that what we learn from receiving a report goes beyond the propositional content of the report.


Michael Gonzalez said...

Can I just say that, over the past several years, I've become more and more attracted to the view that metaphysical modal claims are going to boil down to logical modal claims + "fully understanding what you're talking about". I don't know how to state that second part more formally (I think Swinburne has a similar view and calls it "fully realized" or "fully spelled out" or something like that). I think, taking for granted that we are dealing with normal, competent speakers of English (which I think should literally go without saying), it follows that "Dr. Smith ate the banana" logically entails all sorts of things (the subject is a human with a doctorate, their last name is "Smith", they are not fed exclusively intravenously, etc etc). I think that acknowledging that sort of thing blurs the line between "strictly logical" modality vs. "metaphysical" or "broadly logical" modality (the latter being Plantinga's term).

If we also recognize that objects of different sorts have different characteristic powers/capacities, we are well on our way to a robust theory of alethic modality with much of its grounding in powers. And it is very logically robust because, if (for example) you're talking about a creature that can jump 100ft unaided, you are not talking about a human being.

Alexander R Pruss said...

If the logical claims are *formal* logical claims (as in "q can be proved from p"), then it is very likely that any such account (including Swinburne's) will fall afoul of Goedel's incompleteness theorems.

The problem comes from iterated modals. Consider this obviously true claim:
A. Necessarily (possibly (P or not P)).

But on an account like the above, this means something like:
A*. It can be proved that (a contradiction cannot be proved from (P or not P)).

But that requires being able to prove the consistency of the logical system, which (given some plausible assumptions) will contradict Goedel's second incompleteness theorem.

See: https://philpapers.org/rec/PRUPIN

On the other hand, if the "logical claims" are not formal provability relations, then it is difficult to say what they are if they aren't just metaphysically necessary material conditions.

Michael Gonzalez said...

I'm sure the issue of provability and incompleteness is as intractable an issue for the strictest form of logical modality as it is for mathematics in general. But, what if we just speak in terms of "sense" or "coherence"?

A**. It makes no sense to deny that (it makes sense that (P or not P).

I'm not proposing this to replace strict logical provability, or the formal calculus that accompanies that. But, when we talk about metaphysical possibility, it always seems to come back to what coheres with the facts about (or meaningful descriptions of) the relevant entities; what makes sense to say of a given entity. This will very strongly depend on the characteristic powers of a given type of thing, because, of course, powers are the most relevant facts about a thing vis-a-vis the bringing about of states of affairs (which is what metaphysical claims are all about; where, of course, we include the existence of things among the "states of affairs").

I remember finishing your book on this topic very much attracted to the Aristotelian (powers) + Wittgensteinean hybrid view. But, I'll need to re-read some of it to remember all the details....

In any case, I find this approach (or something like it) to be FAR superior to what is bandied about these days by the likes of Oppy and Malpass. This talk about a common (necessary) origin point, and analyzing "possibility" as just that which branches off at points of indeterminacy is not a modal theory at all. It does not explain or ground possibility; it just gives a picture of possibilities playing out. I'm convinced the only salvageable version of it is just a tacit "powers" theory, since, without first limiting the possible by the powers of the entities in question, ANYTHING could branch off at any point (e.g. at this moment, I could jump 1 foot or 100 feet, and they would share all the same branching history up to this point). What makes one thing impossible and the other possible? The full facts about the entities in question (specifically, yes, their powers).

With this in place, necessity (which is just the inverse of "impossibility" or "non-achievability") is grounded in the senselessness or incoherence of the alternatives. But, this means we can't just assign necessity where it's convenient for us (as Oppy does for the initial state of the natural world). It needs to be reserved for where the alternatives make no sense or don't cohere with the meanings of terms.

Anyway, sorry for the digression. To circle back to the point of this blog post, it seems to me that "Dr. Smith ate the banana" contains within it all sorts of facts about naming, doctorates, etc. If we did not all hold those concepts similarly, then we literally wouldn't know what we were talking about. We might take that string of letters to mean "the banana ate Dr. Smith" or "the Australian accent sounds nice".

Alexander R Pruss said...

I defend the view you don't like in my worlds book. :-)

Michael Gonzalez said...

I'm certain your approach to it is excellent and actually explains/grounds modal issues like possibility. What frustrates me is saying that possibility is MERE branching, which doesn't explain anything. I think you need the powers part to actually limit what could and couldn't happen at a branching point.

Alexander R Pruss said...

Yeah: we definitely need a story about what branches a branching point has and why.