Compositionality without Decomposability
Apple was very quick shipping the (free) replacement adapter.
I've decided to bring order into my thoughts about Fregean thoughts by writing a little paper. If all goes well, I'll hand it in as the termpaper required for my MA. Since my last entry on this topic, I've found out that there is a lively discussion among Frege scholars about the structure of thoughts. Some, in particular Dummett, argue that Frege is, or should be, committed to this view:
ISO) If a sentence A expresses a thought [A], then [A] contains as parts the senses of all meaningful parts of A.
The main argument for ISO is supposed to be some principle of compositionality. Thus Jose Luis Bermudez in [1], p.89f.:
[T]he sense of a complex expression (like a sentence) is determined by the senses of its consituent expressions. The compositionality of thoughts seems to entail that one cannot grasp the thought expressed by a sentence without grasping [...] the senses of the words that go to make up the sentence. From which on can easily derivePRINCIPLE K) If one sentence involves a concept that another sentence does not involve, the two sentences cannot express the same thought or have the same content.
(Bermudez explains that by "concept" he means any senses, not only senses of predicates.) Given a very relaxed usage of "part", PRINCIPLE K implies ISO.
The problem is that in this little argument, the later statements don't follow from the earlier ones.
I think it is reasonable to accept the first statement (and ascribe it to Frege): 1) The sense of a complex expression is determined by the senses of its consituent expressions [together with the structure of the complex expression]. But this implies nothing at all about what is required to grasp the sense of a complex expression. Compare: One might claim that the truth value of a sentence is determined by the extension of its constituent expressions, together with its structure. It doesn't follow that to grasp the truth value True -- whatever that means -- you have to grasp the extensions of all constituents of all true sentences.
What does plausibly follow from (1) is that if you grasp the senses of the constituents of a sentence A, then you are also able at least in principle to grasp the sense of A. But Bermudez' second statement is the converse: 2) To grasp the sense of A, you have to grasp the senses of its constituents. I think this statement is in fact ambiguous. It could mean either
2a) To understand a sentence A, you have to understand its constituents.
or
2b) To entertain the thought [A], you have to grasp the senses of A's constituents, where A is any sentence expressing [A].
(2a) may be acceptable, whether or not it follows from (1). But it does not imply (2b), since understanding a sentence is not the same thing as entertaining the corresponding thought: While reading a Finnish sentence stating that Finnish is a funny language, I might accidentally entertain the thought that Finnish is a funny language, without understanding what I'm reading.
PRINCIPLE K, on the other hand, perhaps follows from (2b), but certainly not from (2a). I'm not even sure if it follows from (2b): Couldn't there be different senses S1, S2 such that it is impossible to grasp S1 without also grasping S2? If so, (2b) would allow that a sentence A involving S1 can express the same thought as a sentence B involving S2 (but not S1).
So I think there is little reason to suppose that the compositionality of senses of complex expressions implies that these senses are in any way really 'composed' out of constituent senses. The complex expression's sense might be determined by the senses of its constituents even though the senses of the constituents are not determined by the sense of the complex expression.
[1] J.L. Bermudez, "Frege on Thoughts and Their Structure", Philosophiegeschichte und Logische Analyse, 2001(4): 87-105.