3.143 The usual form of expression in writing or printing disguises a propositional token’s being a fact.

Because in a printed sentence, e.g., no essential difference appears between a propositional token and a word.

(This is how it was possible for Frege to call a sentence a complex name.)

‘Complex’ here is suggested by Black (p. 103). The others have ‘compounded’ (Ogden) and ‘composite’ (P&McG).

Grammar is invisible. Note also that Wittgenstein thinks it necessary to come up with an explanation for how Frege could have made a mistake.