4.02 We see this from our understanding the sense of a proposition without its being explained to us.
Splutter! We might understand a string of pictographs (women drink beer, say, or bird fly to pharaoh) but we hardly understand a sentence in the same way. We need to know the meanings of the signs. The same is true with pictographs, of course, but they could sometimes be guessed. We could, I suppose, guess the meaning of a sentence, but what could this show us about the essence of propositions? The reason we can understand the sense of a proposition without its being explained to us is that we know the correct use of its signs. In this I include letters as well as words and punctuation marks, since “The dog went Hav! Hav!” is intelligible (that’s the sound the dog made) whereas “The dog went hav hav” would take more guesswork (does “hav hav” mean “pee pee”? is it a place?, etc.). Consideration of the use of writing, including hieroglyphic writing, in fact seems to show that the essence of propositions is not picturing in any simple sense at all. And neither 4.016 nor 4.02 actually denies this.
Proops (pp. 103-105) argues that Wittgenstein is in fact referring back to 4.01 here, when he says ‘this.’ He bases this claim on the fact that it does not make much sense otherwise, and in the Prototractatus 4.02 refers to 4.01 and some related remarks. Presumably Wittgenstein inserted other material without noticing that he needed to change the wording of 4.02.