Full Idea
Thinking can't just be in sequences of English words since, notoriously, thought needs to be ambiguity-free in ways that mere word sequences are not.
Gist of Idea
Language is ambiguous, but thought isn't
Source
Jerry A. Fodor (In a Critical Condition [2000], Ch. 6)
Book Reference
Fodor,Jerry A.: 'In Critical Condition' [MIT 2000], p.64
A Reaction
I think this is a strong argument in favour of (at least) propositions. Thoughts are unambiguous, but their expression need not be. Sentences could be expanded to achieve clarity.