As noted by many who knew or were influenced by Gellner, he was a dying breed: a polymath who was equally adept at philosophy, sociology, antrhopology, and politics. That ability, always noticeable in these essays, is what makes this book so different from like books on the subject.
This is needed because the subject - the problem of relativism in the social sciences - has become such a commonplace one, that one could easily fill a Barnes and Noble with titles adressing it. For all that, one would be hardpressed to count one one hand the books that actually contributed anything useful to the discussion rather than just rehashing the problem while pretending to have original thoughts on it.
I ramble on that for a reason. Gellner's is precisely one of those books that would be counted on that hand. The reason is that he is both a philosopher and an anthropoligist (as most writers in the one discipline ignore the methods of the other). Gellner's philosophic side wants to gravitate towards human universals and in this he resembles Kant and the Enlightenment. His anthropologist side, though, wants to gravitate towards the differences, and in this he takes after Herder and the Romantics.
As those who have read Gellner before know, he sides more-or-less with the Englightenment on this one (never all the way). As a brief synopsis, the first and fourth essay defend positivism and argue that the scientific process not only applies to the 'social sciences' but is the best way for them to operate. The second and (my favorite) third essay, deal with the problem of human universals in a world of seemingly different areas, approaches, cultures and...dare we say it...natures. The fifth, sixth and seventh essay (more antrhopologic theory and less philosophy) deal with and demolish 'structuralism' and 'hermeneutic' approaches to antrhopology with the lattter taking direct aim at Wittgenstien's 'community' theory of language.
While this collection is short (at 187 pages) the insights are fantasitc and as mentioned above, blend the theoretic prowess of the philosopher with the empirical traditon of the antrhopologist. On a personal note, as a longtime fan of Karl Popper, I found Gellners extended critique (first essay) of Popper most useful. Long and short: this book is worth the time, effort, and money.