The following quote relays an anecdote with regards to Piero Sraffa and his influence upon Ludwig Wittgenstein. I’ve hear of a similar story in which Wittgenstein was supposedly sent into a tailspin over a cyclist’s contemptuous gesture that he felt belied his work in the “Tractatus Logico Philosophicus”. Anyways, here it is:
“Wittgenstein was insisting that a proposition and that which it describes must have the same 'logical form', the same 'logical multiplicity', Sraffa made a gesture, familiar to Neapolitans as meaning something like disgust or contempt, of brushing the underneath of his chin with an outward sweep of the finger-tips of one hand. And he asked: 'What is the logical form of that?'” -Norman Malcolm. Ludwig Wittgenstein: A Memoir. pp. 58–59.
Perhaps I’m mistaken, but Sraffa’s gesture to Wittgenstein is not a proposition. By definition, a proposition is a statement that functions as a truth-claim. Sraffa’s gesture is more akin to a negation and therefore a classic Wittgensteinian logical constant. No?