2.4 One could leave van Brakel's discussion of the FP here, but it deserves a bit more analysis, lest it add more confusion to an already confused discussion. We are rather sceptical about such an attitude when it is accompanied by such a thorough lack of technical understanding. But this habit of snappy quotation takes phrases out of context in dangerously misleading ways. Perhaps van Brakel has discovered a new problem that we have to solve. It seems clear that in general, complete characterizations of things, in the sense of necessary and sufficient conditions for them to exist, or correct biconditional definitions of the concepts, cannot be given.
CD is impossible.
We fail to see any problem here. Nevertheless, useful inferences can often be drawn from them. There is no need to have definitions of any of the terms in the formalization. The idea that they should do so, or must in order to achieve some kind of adequacy, is a legacy from the use of logical formalisms to establish the foundations of mathematics, a very different kind of enterprise. It seems likely that most of human conceptual knowledge is of this character.