# Tarski, Wittgenstein and Undecidable Sentences in Affine Relation to Gödel’s. Thought of the Day 65.0

I imagine someone asking my advice; he says: “I have constructed a proposition (I will use ‘P’ to designate it) in Russell’s symbolism, and by means of certain definitions and transformations it can be so interpreted that it says: ‘P is not provable in Russell’s system.’ Must I not say that this proposition on the one hand is true, and on the other hand is unprovable? For suppose it were false; then it is true that it is provable. And that surely cannot be! And if it is proved, then it is proved that it is not provable. Thus it can only be true, but unprovable.” — Wittgenstein

Any language of such a set, say Peano Arithmetic PA (or Russell and Whitehead’s Principia Mathematica, or ZFC), expresses – in a finite, unambiguous, and communicable manner – relations between concepts that are external to the language PA (or to Principia, or to ZFC). Each such language is, thus, essentially two-valued, since a relation either holds or does not hold externally (relative to the language).

Further, a selected, finite, number of primitive formal assertions about a finite set of selected primitive relations of, say, PA are defined as axiomatically PA-provable; all other assertions about relations that can be effectively defined in terms of the primitive relations are termed as PA-provable if, and only if, there is a finite sequence of assertions of PA, each of which is either a primitive assertion, or which can effectively be determined in a finite number of steps as an immediate consequence of any two assertions preceding it in the sequence by a finite set of rules of consequence.

The philosophical dimensions of this emerges if we take M as the standard, arithmetical, interpretation of PA, where:

(a)  the set of non-negative integers is the domain,

(b)  the integer 0 is the interpretation of the symbol “0” of PA,

(c)  the successor operation (addition of 1) is the interpretation of the “ ‘ ” function,

(d)  ordinary addition and multiplication are the interpretations of “+” and “.“,

(e) the interpretation of the predicate letter “=” is the equality relation.

Now, post-Gödel, the standard interpretation of classical theory seems to be that:

(f) PA can, indeed, be interpreted in M;

(g) assertions in M are decidable by Tarski’s definitions of satisfiability and truth;

(h) Tarskian truth and satisfiability are, however, not effectively verifiable in M.

Tarski made clear his indebtedness to Gödel’s methods,

We owe the method used here to Gödel who employed it for other purposes in his recently published work Gödel. This exceedingly important and interesting article is not directly connected with the theme of our work it deals with strictly methodological problems the consistency and completeness of deductive systems, nevertheless we shall be able to use the methods and in part also the results of Gödel’s investigations for our purpose.

On the other hand Tarski strongly emphasized the fact that his results were obtained independently, even though Tarski’s theorem on the undefinability of truth implies the existence of undecidable sentences, and hence Gödel’s first incompleteness theorem. Shifting gears here, how far was the Wittgensteinian quote really close to Gödel’s? However, the question, implicit in Wittgenstein’s argument regarding the possibility of a semantic contradiction in Gödel’s reasoning, then arises: How can we assert that a PA-assertion (whether such an assertion is PA-provable or not) is true under interpretation in M, so long as such truth remains effectively unverifiable in M? Since the issue is not resolved unambiguously by Gödel in his paper (nor, apparently, by subsequent standard interpretations of his formal reasoning and conclusions), Wittgenstein’s quote can be taken to argue that, although we may validly draw various conclusions from Gödel’s formal reasoning and conclusions, the existence of a true or false assertion of M cannot be amongst them.

# Whitehead’s Anti-Substantivilism, or Process & Reality as a Cosmology to-be. Thought of the Day 39.0

Treating “stuff” as some kind of metaphysical primitive is mere substantivilism – and fundamentally question-begging. One has replaced an extra-theoretic referent of the wave-function (unless one defers to some quasi-literalist reading of the nature of the stochastic amplitude function ζ[X(t)] as somehow characterizing something akin to being a “density of stuff”, and moreover the logic and probability (Born Rules) must ultimately be obtained from experimentally obtained scattering amplitudes) with something at least as equally mystifying, as the argument against decoherence goes on to show:

In other words, you have a state vector which gives rise to an outcome of a measurement and you cannot understand why this is so according to your theory.

As a response to Platonism, one can likewise read Process and Reality as essentially anti-substantivilist.

Consider, for instance:

The phenomenological ontology offered in Process and Reality is richly nuanced (including metaphysical primitives such as prehensions, occasions, and their respectively derivative notions such as causal efficacy, presentational immediacy, nexus, etc.). None of these suggest metaphysical notions of substance (i.e., independently existing subjects) as a primitive. The case can perhaps be made concerning the discussion of eternal objects, but such notions as discussed vis-à-vis the process of concrescence are obviously not metaphysically primitive notions. Certainly these metaphysical primitives conform in a more nuanced and articulated manner to aspects of process ontology. “Embedding” – as the notion of emergence is a crucial constituent in the information-theoretic, quantum-topological, and geometric accounts. Moreover, concerning the issue of relativistic covariance, it is to be regarded that Process and Reality is really a sketch of a cosmology-to-be . . . [in the spirit of ] Kant [who] built on the obsolete ideas of space, time, and matter of Euclid and Newton. Whitehead set out to suggest what a philosophical cosmology might be that builds on Newton.