5.523 The symbol of generality occurs as an argument.

OK, that’s how it appears in the notation. See Letters to Ogden p. 49: “Here I want to use symbol and not symbolism because I refer to the variable x or y etc. in (Ex, y)… and not to the whole complex of symbols as before. I own this is very dark but please leave “symbol” here and don’t make it uniform with 3.24.”