At 195B 9 it is pointed out that the Wax Block theory does not cover that large class of judgments in which no sense-objects are concerned, e.g. judgments about numbers. How can we make the mistake of judging that 7 + 5 = 11?

The simile of the Aviary, now introduced, is very simple. It illustrates the difference between potential (or latent) knowledge and actual knowledge, i.e. between knowledge at our disposal, because it has been learnt and stored away in the mind, and knowledge present and ‘alive’ at the moment. The theory is that when we make a mistake about the sum of 7 and 5 we are ‘hunting for’ the knowledge of 12, which we ‘possess’ (κεκτ⋯σΘαι) as we might possess a bird in a cage, but which we have not ‘got about us’ (ἒχειν); but we mis-take, wrongly take our knowledge of 11, i.e. we call up before our mind a different piece of knowledge.