1 Frege on thoughts

Frege is concerned with separating logic from psychology. In addressing such separations, he coins a very important concept in the history of analytic philosophy: the concept of a proposition.

Frege calls a thought what we would now call a proposition. When he talks about thoughts, he doesn’t want to talk about mental states, but about what we may call their content. For instance, the content of the belief that grass is green is the thought (proposition) that grass is green, rather than the thought (proposition) that the sky is blue.

For Frege, one of the key features of a proposition is that it is capable of being true or false. He also thinks it has some further features: “The thought, in itself immaterial, clothes itself in the material garment of a sentence and thereby becomes comprehensible to us. We say a sentence expresses a thought.”

For Frege, propositions are immaterial objects, and can be the contents of mental states. They are also the contents of declarative sentences, and are the kind of thing that can be true or false. Sentences can also be true or false, but they are only so because they contain a proposition. For this reason, we could say that a proposition is the only kind of thing that is necessarily truth-evaluable, and, moreover, we could say that a proposition is the kind of thing that has its truth conditions essentially: a sentence could have had another meaning, and this had been the case, it could have had different truth conditions. A proposition necessarily has the truth conditions that it actually has.

For instance, compare the sentence ‘grass is green’ with the proposition that grass is green. The first could have meant something else; for instance, it could have meant that there are owls in the attic, in which case it may not have been true even if grass was green. But, necessarily, the proposition that grass is green is true whenever grass is indeed green.

Different sentences may express the same proposition, even if somehow the sentences manage to express something above the proposition. For instance, ’Maria is happy but tired’ expresses the same proposition as ’Maria is happy and tired’, yet the first sentence gives us the impression that being tired is somehow opposed to being happy, while the second one doesn’t. Or consider the case in which I say, today, that the birds are flying, and I wish to describe this same fact tomorrow. I would have to say that yesterday the birds were flying. But the two sentences express the same proposition, since ‘yesterday’ and ‘today’, as used in these two sentences, refer to the same center.

On the other hand, the same sentence may express different propositions depending on who says it. This is the case of sentences like ’I like cats’. Said by A, it will express the proposition that A likes cats, but said by B, it will express the proposition that B likes cats.

More relevant to the topic of the course, Frege argues that propositions are not identical with token mental states. The latter is what he seems to have in mind when he talks about ideas: sense impressions, feelings, moods, inclinations, etc. He offers a more precise characterization of ideas:

(1)

Ideas cannot be perceived by the senses.

(2)

An idea which someone has belongs to the content of her mind.

(3)

Ideas need a bearer, they cannot exist independently. We could also say that ideas are not substances.

(4)

Every idea has only one bearer, no two people have the same idea.

This characterization makes it seem plausible that when Frege talks about ideas he is talking about token mental states: token mental states can’t be perceived by the senses, though they may have phenomenal qualities (e.g. qualia); we could say, in a somewhat dualist-friendly terminology, that a token mental state belongs to the contents of one’s mind; token mental states do not exist independently of their bearers, and crucially, token mental states exist can’t have more than one bearer: even if we are having very similar sensations, my particular sensation is not the same as yours, mine is in my head, and yours is in yours.

With this in mind, it’s easy to understand Frege’s argument that propositions can’t be ideas. Propositions are the kinds of things that can be grasped by many people: we want to say that people can have the same beliefs, or the same desires, but when we say this we are not saying that they can have the same token mental state. Rather, we are saying that they have beliefs or desires with the same contents. And these contents are propositions. Since propositions can be grasped by more than one person, but ideas can’t be had by more than one person, propositions are not ideas.

Frege states this line of reasoning as follows:

It’s hard to see how one may show that in fact the content of my belief is the same as yours, so Frege uses an indirect path. He argues that if propositions were just ideas, we wouldn’t be able to make sense of a lot of our practices. In particular, we wouldn’t be able to make sense of disagreement, rational disputes, and scientific practices. For all the time each of us would only be talking about something accessible only to her, and this kind of thing can’t be shared by anyone.

The relation we stand to thoughts (propositions) is not the relation of having them, but of grasping them. For the rest of the paper, Frege describes some other features that he takes propositions to have: they have their truth values eternally, they remain unchanged by our communicative acts or by our grasping them, and they belong to a third realm that is neither the external nor the inner world. We won’t examine all the other properties that Frege attributes to propositions. Instead, we will revisit some previous discussions with this new notion in mind.

2 Intentionality

In his paper “On sense and reference”, Frege explores the nature of proper names. This is not strictly related to our current topic, but is important to keep in mind because of the claims he makes there about propositions. We have already seen the following kind of example, but it won’t hurt to examine it again. Consider the following sentences:

(1)

Hesperus is a planet.

(2)

Phosphorus is a planet.

Since Hesperus is the same thing as Phosphorus, (1) is true if and only if (2) is true. But consider the following sentences:

(3)

Kate believes that Hesperus is a planet.

(4)

Kate believes that Phosphorus is a planet.

(3) may be true and (4) false, even though Hesperus and Phosphorus name the same thing.

However, the following principle seems to be a good one:

Compositionality:

The proposition expressed by a sentence is a function of the semantic contents of its components, together with their syntactic arrangement.

Because (3) and (4) have different truth values, and so, express different propositions, and since the only difference between them is the fact that ‘Hesperus’ appears in (3) and ‘Phosphorus’ in (4), Frege concluded that the semantic contribution of these names could not be just their referent, but that it had to be something else. Frege called this the sense.

Though it might be controversial to claim that senses are just definite descriptions, we will assume that here. So, for instance ‘Hesperus’ will contribute the description the evening star, and ‘Phosphorus’ will contribute the description the morning star, even though they both refer to Venus (since Venus is the thing that people used to call Hesperus and Phosphorus).¹ Thus, according to Frege, the propositions expressed by (1) and (2) would be (4) and (5), respectively:

(5)

The morning star is a planet.

(6)

The evening star is a planet.

Once we substitute (5) and (6) in the that-clauses in sentences (3) and (4), respectively, we get the result that we wanted, namely, a difference in truth value between (3) and (4).

Frege and others (most famously, Bertrand Russell) thought that this kind of view of propositions would also allow to explain the truth of propositional attitudes that involved expressions without a referent, like ‘Sarah believes that baby unicorns are cute’. The word ‘unicorn’ doesn’t have a referent, but it has a sense, perhaps something like ‘white horse with a horn that likes to hang out with young ladies’.

Because Frege thought that that-clauses denote the proposition ordinarily expressed by the sentence in it, we now call sentences like (3) and (4) propositional attitudes. For reasons we’ll leave unexplained, very few people accept Frege’s account of propositions and propositional attitudes these days. The important thing is that a lot of people have thought that whatever account we give of the content of beliefs, desires and the like, must yield the appropriate results in our examination of propositional attitudes.

Brentano was not around when Frege introduced this notion of proposition, but Chisholm definitely seems to have Frege’s work in mind when he refines Brentano’s thesis that intentionality is the mark of the mental. We may think that propositions, or the content of a propositional attitude, is whatever kind of content it has to be to account for the data we just examined.

Now it’s all clear!

What Dretske, Millikan and Brandom were trying to do, each in their own way, was to explain how our mental states can have the contents that they actually have, and in particular, how they can have the kind of contents that would explain the data about propositional attitude ascriptions.

Dretske argues that it’s not all that hard to account in purely causal terms for the difference between attitude ascriptions involving coreferential expressions, as long as the expressions in the sentence indeed have a referent. His main problem comes when he has to explain attitudes that involve inexistent objects, like unicorns. He thinks we can start solving this problem by examining first the problem of misrepresentation, or how it is possible that someone has a propositional attitude towards a false content.

Millikan is also trying to solve this problem. Her view is similar to Dretske’s in that it appeals to the notion of a biological function, though the details are very different. She accounts for the problem of representation in terms of the notion of a proper function.

Dretske and Millikan are trying to explain how it is that our mental states can have the kind of content that would fit the data from propositional attitude ascriptions. Moreover, they are trying to do it in a way that posits only as much as our best science.

Brandom engages in a similar kind of project. He also wants to explain how our mental states can have the kind of content that would fit the data. But he does it in a radically different way. Dretske and Millikan accept Frege’s view that propositions are the kinds of things that are truth-evaluable, where truth-evaluability seems to involve something like the notion of representation. A proposition is true only if what the proposition represents obtains.

Brandom doesn’t like this picture. He thinks that the main picture we should use to understand content (both mental and linguistic) is the notion of an inference, or a process that starts with a particular content and ends with another. In a way, what Brandom ultimately tries to argue is that the very notion of representation on which accounts like Dretske’s and Millikan’s rest is not exactly what we need. It makes too many unwarranted metaphysical commitments, and so he attempts to deflate the notion of representation by examining the expressions we use to talk about representation.

His hope is that, in doing this, we will end up having a complete account both of the kinds of contents that mental states must have, and how these contents manage to represent something or other.