5. 515 It must be apparent in our symbols that what is connected with one another by “v”, “.”, etc. must be propositions.
And this is indeed the case, because the symbol “p” and “q” itself presupposes “v”, “~”, etc. If the sign “p” in “p v q” does not stand for a complex sign, then it cannot have sense on its own; but then also the signs “p v p”, “p. p”, etc., which have the same sense as “p”, could have no sense. If however “p v p” has no sense, then also “p v q” can have no sense.
So p must be a proposition, a complex sign.
Black (p. 279) writes: “The German text is puzzling and may have been printed incorrectly. I suggest (as an alternative to P.& McG.) that the remark might read: ‘And this is so, for the symbol p in p v q itself presupposes “v”, “~”, etc.”