Carnap, Kripke, presupposition

This is an expansion of a Carnap/Kripke angle on the connection between metaphysics and presupposition.

It is generally accepted that Kripke in some way conclusively showed that the notion of analyticity does not coincide with that of ("metaphysical") necessity, and hence put a few nails in the coffin of Carnap's philosophy.

There is in this no discussion of whether the concepts as understood by Kripke are the same concepts as those used by Carnap.  It is just assumed that these concepts have a single definite meaning and that Kripke showed that the two differed in extension (and hence in meaning).

What seems not to be mentioned is that Carnap, far from carelessly identifying the two concepts actually defines necessity in terms of analyticity, and gives cogent reasons for doing so.

There is no carelessness here, and it is immediate that if Kripke's arguments are sound, then he must be using different concepts.

So where do tbe presuppositions come in?

Well first I have to give another account of how it is that necessity (metaphysical and logical) and analyticity coincide.

A sentence is analytic if its truth in every possible circumstance is a consequence of the semantics of the language.  And if the language is for talking about the real world (rather than perhaps some abstract domain), then that means in every possible world (and hence we see immediately the connection with necessity).
But it is essential here that the semantics does provide a complete account of the truth conditions of the language.
In respect of an incomplete semantics then some sentences will not be analytic even though they may be true in every possible world.

Kripke introduces the notion of rigid designator.
These are supposed to designate the same entity in every possible world.
Consequently every true identity between rigid designators is necessary.
And it is held that these identities are not analytic (I have never actually seen an argument to that effect).

But this assumption is tantamount to the assumption that the semantics gives an incomplete account of the truth conditions for sentences in the language.
Even Quine, following his explanation of analyticity in "Two Dogmas" would have to agree that identities between rigid designators are analytic, for he allows that in judging analyticity we may use any information "about the language" but none about the world, and that two designators rigidly designate the same entitity is surely a fact about language not about this (or any other) world.

So here come the presuppositions (and the meaning postulates).

This tells you about how you have to go about formalising the semantics of language.
To give a complete account of the truth conditions of a sentence you must define a function whose domain is the possible worlds which yields the truth value of the sentence in each possible world.
This means that you have to define the set of possible worlds.
Carnap would not put it this way, but we could say that metaphysics is a stage in defining the semantics of a language.

For Carnap of course, defining this domain of possible worlds (states of affairs) is what his meaning postulates are for.
But we could also go with Collingwood, and talk of these constraints on the domain of the truth conditions as "absolute presuppositions" embedded in the language.

Personally, the introduction of meaning postulates by Carnap is not something I greatly care for, but I see that his decisions on what he called "language planning" and his semantic methods forced him into it, and to avoid them you need to start almost from scratch.

Meaning postulates were a sticking plaster made necessary by Carnap's failure to notice the flaw in Wittgenstein's account of logical truth in the Tractatus (which consists is asserting that atomic propositions are logically independent, as if there could be no logical relations between predicates).
Bear in mind here that neither Wittgenstein nor Carnap has a narrow conception of logical truth (as is standard now) both intending logical truth to exhaust the non-empirical and hence correspond with analyticity (suitably defined).

The connection between Carnapian necessities and presupposition would be too tenuous to be worthy of mention, were it not in the context of Collingwood, for in this context it makes a connection between Collingwood's conception of metaphysics and the concept of metaphysics Carnap might have had, if he had allowed himself a slightly more liberal use of the term.
(noting that nothing here disturbs the fact that Carnap has defined metaphysics out of existence, the meanings postulates, are not for him metaphysics, not even if they include large cardinal axioms to fix the meaning of the concept of set).

Roger Jones