This is a tremendously intelligent and well-written book. The depth and breadth of Gellner's knowledge are truly impressive. That said, I think the book is wrong-headed in at least two major ways.

Most importantly Gellner assumes that the historical-cultural situation of a society is perfectly reflected in the intellectual and psychological make-up of its citizens. He maintains this belief in spite of evidence to the contrary (e.g., that Wittgenstein never talked about culture or politics, that he was amazingly poorly read in the relevant texts, or that the Tractatus is a seamless extension of the Cartesian empirical tradition). Gellner seems to believe in an osmosis theory of learning, given the lack of evidence that people actually knew or believed things, and so he constantly falls back on ideas "being in the air" or things that "surely everyone knew."

This is some sort of Historical Distance Fallacy. Surely no one (no academic) would think it possible to reduce the social, cultural, political issues of present day America to a definitive description only a few pages long and then assume that this description was also a description of the mind of some randomly-chosen individual. (And if this is not applicable to randomly-chosen individuals, then Gellner needs to make some additional arguments as to why it applies to any specific person.)

The second weakness is that I believe Gellner completely misinterprets Wittgenstein's later work (i.e., the position he takes in Philosophical Investigations). Gellner claims that Wittgenstein replaced the logical atomism of the Tractatus with a cultural determinist/relativist position based in a romantic view of the peasantry. He believes in spite of his admission that Wittgenstein never talked about such things.

It seems to me that the view in the Tractatus was, as Gellner describes, one in which words limited what the world was. In the empiricist tradition, basically you can't get beyond the words to the world "itself." My view of the transition is that Wittgenstein shifted from this view (that words both created and limited reality) to the idea that language was something that people used as they interacted with the world. This is a shift from "given that we know we have language, what can we say about the world?" to "given that we live in the world, what can we say about language?" This is why Wittgenstein seems so obsessed with tools and workmen and it ties in to the story told about the conversation he overheard on the train in which a "meaningless" remark was understood and used in conversation.

Gellner seems to think that the Philosophical Investigations doesn't allow for error or critique, but I think that all it excludes is philosophical critique of the sort that philosophers love to engage in which allows them to claim that engineers or botanists or carpenters "don't know anything."