He is critical of the PLA.
(p.75): "It would not be (logically) possible to frame concepts only on the basis of one's own (private) experience; if the signs in which such concepts were supposed to be embodied constituted a 'private language' in this sense, they would not have any meaning even for their author himself"
Comment: This is a satisfactory summary of the conclusion.
(p.78): "It can be conceded that a causal condition of my coming to understand the use of the English word 'pain' consisted in the fact that when I felt pain, as a child, I behaved in ways that my elders took to be the expression of it. This does not, however, in the least prevent me from drawing a present distinction between my feelings of pain and the behaviour which expresses them, so that when I ascribe pain to myself I refer to the feeling and not to its manifest effects."
Comment: Ayer here argues, as Pears does (his 'C-subtle'), that the teaching links are important, but need not be the *sole* repository of meaning for 'pain'. We can begin with the teaching links, and then later shift the meaning (to various extents) away from the context in which it was learned.
Ayer's main argument (p.76) is based, I think, on the perception that Wittgenstein is a direct realist. If, for example, every individual is unable, on their own, to establish a meaning for a symbol, using their sensations, then he argues that having many people equally impotent does not help. Zero multiplied by a hundred is still zero. Similarly, if every individual loses confidence in their ability to make "an act of primary recognition" - judges that they can no longer rely upon "corroboration of a memory...by an item of sense-experience" then no amount of cross-checking will assist - "everything hangs in the air".
Wittgenstein would - I think - refuse to accept Ayer's argument, because he refuses to accept the perspective from which it is made. His epistemology is robust common sense. There is no problem identifying public objects - we just see them. Sometimes we make mistakes - but that doesn't imply anything alarming about the directness of our experience of reality. Individuals aren't on their own. They know what other people are thinking and feeling - though sometimes they make mistakes.