They are used in conjunction with the fundamental questions in the Theory of knowledge to develop more cohesive and complete epistemological constructions. How does the truth value of a proposition realte to ones knowledge of that statement. He firstly, differentiates between the Theory of Knowledge and the areas of Lexicography and Scientific inquiry. Epistemology one must remember ius neutral with respect to particular matters of fact unlike scientific inquiry. It is neither proved by formal demonstration as in mathematics nor is it tested by observation as in mathematics.
Epistemology is simply an analysis and clarification of propositions or families of propositions.
Scepticism, being the bane of most philosophies should be dealt with first. For all p, for all you know, you don't know p. This is in fact problematic. Even the weak from should produce grounds for doubting Ayer's thesis, especially in the case of something that is warranted by experience. In short Ayer's method of analysis includes a case by case consideration of each proposition as it appears to him and a similar refutation of the sceptic.