2.18 What every picture, of whatever form, must have in common with reality in order to be able to picture it at all -- rightly or falsely -- is the logical form, that is, the form of the reality.

Or perhaps: the form of reality. Wittgenstein seems to use Wirklichkeit to mean "bit of reality", so that one can (and he does) distinguish between this and that reality (as here, I think) and the totality of reality (as in 2.063). Nothing really new here. Except the idea of “logical form.” Ostrow (p. 47), following Burton Dreben, suggests that the point of the notion of logical form is to ease us into the idea that written propositions are pictures of reality, even though they do not appear to be (see 4.011). Otherwise the concept of pictorial form would seem to have been pointless – Wittgenstein could just have referred to logical form throughout. On the same page, Ostrow rejects Friedlander’s suggestion that logical form is more general and additional to the pictorial form, on the grounds that the nature of the generalization in question would be unclear, and (see note 2 on pp. 144-145) that 2.181 implies that it makes sense to speak of cases in which the pictorial form is the logical form, whereas Friedlander treats them as corresponding to very different dimensions of the picture.