The prose of Mr. Frankfurt is in this book as terse, concise and understandable as in previous works ("taking us seriously and getting it right", "on truth"), which does not mean hastily construed, as it is evident from the density of information and the carefulness of the choice of words that he has given long thoughts on the subject he reflects upon. So, as stated in the title of this review, it is delightful to read his essays in general, and this one in particular, which have the added benefit of not being cluttered with countless quotes and references, as so many philosphers today feel compelled to do (a vice specially conspicuous in European thinkers). There are a few of those quotes and references (St. Augustine and Bernard WIlliams come to mind), but always relevant and well serving the purpose of illuminating the main line of argument, instead of calling our attention to the erudition of the author.
As for the content, that's the dispiriting fact, as the central thesis of the book is that traditional rationalist philosphies have got it wrong in trying to identify normative reasons that would authoritatively dictate how we should act (and, by extension, how we should live). As he states brilliantly in section 10 of the first chapter, to be able to ascertain the validity of those reasons of how to live we should have previously agreed on what kind of live is (objectively) valuable to pursue, so the whole argument suffers from an unavoidable circularity that makes the intent of finding those reasons (or answer the question they seek to settle rationally) necessarily bound to fail. We'll come back later to the implications of that inability of reason to help us determine the ultimate ends of our lives (which is not in itself original). Mr. Frankfurt contends in the rest of the book that asking for the ultimate reasons to live is getting the causality backwards, as instead of having reasons to care for things as ends in themselves what we find ourselves with is objects of our interests that we care about (being love the higher degree of caring that can exist) which in turn, because of them being important to us, give us reason to act in a certain way.
All of that is well and good, and in line with some emotivist descrptions of normativity that can trace it's origins back to Hume (if not further, as it can be argued that Epicurus already held similar views four centuries BC).
The more orignal part of the book is developed in the third chapter, where Mr. Frankfurt argues that the higher form of love, and a precondition for truly loving anything (thus truly caring about, and because of that, truly having reasons to act in certain ways) is self-love. I'm afraid I found this part less persuasive than the rest, as the self-love it postulates ends up seeming to be little more than a contrivance to justify having a reason to care for something in the first place (as both from stoic and buddhist stances it could be argued that it would be better for men not to love anything, as it causes us to be attached to things over which we have no control).
A final word about the consequences of assuming the inability of a universal (or objective, or even intersubjective) reason to provide us with the ultimate ends we should pursue: if that were the case (and I repeat that Mr. Frankfurt book makes one of the best laid out arguments I've read so far for it) it would be impossible to adjudicate between competing claims made by different individuals, as each could defend those claims by stating they were acting in the best interest of what they most deeply care about, and those inerest would be incommensurable. So for example, we would have no rational argument to defend that loving a racial minority (and thus acting to improve their lot in life) is morally superior to hating that same minority (and thus working to extermiante it, as hate could be construed as a love for the disappearance of that particular group). The members of the Frankfurt school (so called because of the German city that originally hosted the Institute of Social Studies with which most of them were associated, nothing to do with the author we are considering here) are just one example of thinkers who, after denouncing the inability of the scientific-technical (or instrumental, or sujective) reason to provide us with ultimate ends, spelled out the need for practical philosophy (or ethics) to devote its energy to that quest (the quest for a rationality that had something to say about our ultimate ends, the ends that are not means to attain anything else). If that quest is doomed, ethic is impossible, and moral discourse is irrelevant.
Although Mr. Frankfurt admonishes us in his final paragraph to bear that irrelevance with good humour, and his brilliant book gives us much to think about, all I can say is that I still do not find the overall description of our human condition satisfactory, although of course that goes well beyond the opinion that this very fine piece of work deserves.