Meaning and Truth

Course Notes

(6) Thought and Indexicality

(A) Criteria for Sameness of Thought

Uncharacteristically, perhaps, Frege nowhere gives a definitive criterion for sameness of thought (= sense of a proposition). There are just two passages (both written around the same time, 1906) where he seems to offer his most careful formulation, but the two criteria he suggests appear to conflict. In a letter written to Husserl, Frege provides the following ‘objective criterion’:

• (SLE)  Two propositions A and B possess the same sense (express the same thought) iff ‘both the assumption that the content of A is false and that of B true and the assumption that the content of A is true and that of B false lead to a logical contradiction, and ..... this can be established without knowing whether the content of A or B is true or false, and without requiring other than purely logical laws for this purpose’. [FR, pp. 305-6.]

Elsewhere, however, Frege offers a slightly different criterion:

Whilst (SLE) clearly bases sameness of sense on logical equivalence, (SEE) appears to ground it on epistemic equipollence. The conflict seems to be between a fairly coarse-grained notion of sense, bringing it much closer to the notion of Bedeutung (and echoing Frege’s earlier notion of ‘conceptual content’), and a much finer-grained one. The best, I think, we can offer, tightening up (SLE), but not going so far as (SEE), is the following criterion:

On this criterion, arguably, the two members of a contextual definition do possess the same sense, whilst, say, ‘The Morning Star is visible in the morning’ and ‘The Evening Star is visible in the morning’ do not, which is, I think, how Frege would have wanted it.

(B) The Problem of Indexicals

Indexicals or demonstratives are expressions such as ‘I’, ‘You’, ‘here’, ‘there’, ‘now’, ‘then’, ‘this’ or ‘that’, whose reference depends systematically on the context; and they pose a serious problem for Frege’s conception of sense. For if the reference changes, then so too must the sense (as ‘mode of presentation’ of that reference). Consider the following:

(TS)   Today is sunny.

Uttered today, this clearly expresses a different thought from that that would be expressed if uttered tomorrow; so the sense of ‘today’ (as partly determining the thought) must differ on the two occasions. Yet there seems to be some element in the meaning of each indexical that remains constant. Let us call this its linguistic role. I understand the linguistic role of an indexical if I understand the rule that takes me from the context of utterance to the object referred to. Then Frege is to be understood as denying that the sense of an indexical is its linguistic role. But then what is it?

Here is one suggestion as to how (TS) might be understood:

(DS)   Wednesday 24 March 1999 is sunny.

But it is clearly possible to hold (TS) as true but (DS) as false, and vice versa, and hence, by the criterion (SCE) above, they must be taken to express different thoughts; and the same will apply to any attempt to ‘cash out’ the indexical in terms of a definite description (cf. the problem of ‘simple’ names), a problem that has been called (by John Perry) the problem of the essential indexical. The only alternative might seem to be to take the sense of any indexical as used on a given occasion as primitive and irreducible. But this threatens us with a proliferation of once-only senses. Carried to its logical conclusion, the following sentence would express different thoughts for every different person at every different point in space at every different moment in time:

(IHN)   I am here now.

It is clear, however, that Frege allowed that the thought expressed by (TS) uttered today could be expressed on other occasions. To express tomorrow what I said today, I would have to utter:

(Y1S)   Yesterday was sunny.

Indexical thoughts are ‘dynamic’ thoughts, and here the ‘mode of presentation’ of the object is a ‘way of keeping track’ of it (to use Gareth Evans’ terms), requiring a continual process of indexical intersubstitution. But how far can this go on? Next Wednesday, I might say:

(Y7S)   The day before the day before the day before the day before the day before the day before yesterday was sunny.

Yet there is obviously a better sentence:

(LTS)   Last Wednesday was sunny.

This introduces the concept day of the week, but remains indexical. But surely at some point, e.g. in a few years’ time, I am going to end up using (DS) to express the thought, and then we seem to be back with the dilemma. Of course, even this is implicitly indexical (i.e. it presupposes the Christian calendar), but we do seem to have been led to an arguably different thought.

However, just as in the case of ‘simple’ names, we can make use of a scope distinction to resolve the difficulty, insisting here only on (SWT):

The use of the indexical ‘I’, however, is more of a problem for Frege, since he does talk of being presented to oneself in a ‘special and primitive way’, which would suggest that there are some kind of thoughts – (necessarily private) thoughts about oneself – that no-one else can share; which clearly conflicts with his usual insistence that thoughts are objective. However, my own view is that this simply reflects a residual and misguided Cartesianism, and that we should indeed adopt the same strategy here as in the case of other indexicals (with certain allowances made for the ‘expressive’ use of ‘I’).

© Me

Today

24 March 1999

Meaning and Truth

Mike Beaney