4.12 The proposition can present the whole of reality, but it cannot present that which it must have in common with reality in order to present it—logical form.

In order to present logical form, we would have to be able to put ourselves, along with propositions, outside logic, that is to say outside the world.

Is “logical form” then unthinkable? It is unpresentable, unrepresentable. What might we take it to be? Obviously an unknown something that propositions have to share with reality in order to represent it. But this x the unknown has now become an unthinkable unknown. From a logical point of view there cannot be any foundations or prerequisites for logic. Outside a logical point of view we cannot think about logic qua logic. So hypotheses about the evolution of the brain cannot tell us anything [relevant] about the law of excluded middle, for instance. If it is a biological contingency that we recognize logical necessity this does not make it less necessary. So ideas about the foundations of logic are either extra-logical or themselves logical. The theory of logic, or the philosophy of logic, the metaphysics of logic, is either something irrelevant such as biology or psychology, or else it is merely logic itself. Or else it is a hopeless muddle.

McManus pp. 94-95: “When we imagine ourselves identifying a logical form that a proposition must possess in order to represent a particular possible fact, we can only latch on to something that might impose a superficially intelligible (pseudo-) requirement by staying ‘within logic’: that is, by using a proposition that picks out the thus-and-so of the imagined logical form—an object’s being in a particular spatial location, say. But such an identification takes for granted that we understand how this state of affairs must be represented, that its logical form is such that it must be represented using a proposition that captures an object’s being spatially located. But now the ‘requirement’ exposed is that possible facts that are characterized like this must be … characterized like this. Our quest for a genuine requirement must drive us, it seems, ‘outside logic’, and with it, outside any presupposed frame of reference with which to characterize the world. Our ‘indication’ of the logical form now becomes an inarticulate pointing at a bare that, about which we now find that we cannot ask the sort of question of con-formity which we set out to ask.”

There is, McManus argues, no similarity as such, nor sharing of the same form as such. Things are only ever like or unlike in some or other particular respect. What is like what then depends on how we look at things, on how we choose to categorize or characterize things.