My father bought me this book nearly forty years ago (then a new publication, and my father was admin-ing in a leading English university, where he had valuable contact with academic staff). I was about to enter college to study music. It was as indispensible to me then as now 40 odd years on, even though I wasn't studying composition at the time. It was invaluable in helping me to understand the language behind 20th century composition, as well as compose contemporary music that could stand up to critical scrutiny by tutors, some of whom were established composers themselves. When I lost the volume during my relocation, I truly felt I'd lost the most important element of my toolkit. And I simply had to have a replacement!!!
There is just so much in the volume and so inspirational in its delivery - sporting exercises, copious listening lists etc at the end of every chapter and a wealth of musical examples within them. One of its best qualities has to be that it has such a beautifully succinct narrative, without any fatuous waffling about merits or demerits of this or that or the politico-economic climate of the times as the language evolved! It simply gets on with the job of giving you what there is out there, how to understand it technically, and how to shape your own technical understanding and aesthetic approach by "doing it" (ie composing music yourself). As the author beautifully puts it, the tools are given here; all the aspiring composer needs now is creativity!! Indeed if you can't compose while dipping through this wonderful volume (because it teaches more than JUST harmony!!!) then I don't think you would have that necessary creativity to compose at all. The book is also impeccably put together, so that you don't have to read from cover to cover in order to develop your musical/compositional vocabulary - well, I'd recommend first getting to grips with the initial concepts of the impact of different intervals, the chiaroscuro of chordal formations etc etc etc.
This is a truly opulent volume, and if you have no other book than this, you would still be able to compose, even if you teach yourself through it!
There are just two little criticisms though:
(1) Like so many music books, it fails on providing for the listening element. I would want the publishers to perhaps produce an optional enhanced volume comprising 2 CDs, accommodating (a) all the musical examples and (b) a representative sample of the recommended listening list. This editorial enterprise would greatly add to this volume. Or alternatively, create a dedicated website with such listening samples (such as Alex Ross's "The Rest is Noise" or David McCleery's "Discover Classical Music of the Twentieth Century (Book & Website with music)"). Twenteth century scores are not easy to read, and the book assumes that you would have accomplished keyboard skills to play the examples. Well, not all competent composers are keyboardists. (I mean, even Ralph Vaughan Williams admitted that the piano was a continual mystery to him.)
(2) It is such a great pity that this volume was never updated to cover the latter end of the 20th century. But nonetheless it will have its niche carved out among the other great historical volumes, like Schoenberg's "Fundamentals of Music Composition" (Persichetti himself is a composer of course). Rimsky Korsakov's "Orchestration" etc etc.
IMHO this book should be mandatory to all compositional courses, and I can't recommend it highly enough!!! It's the best under-twenty-quid I've ever spent, and I will make sure there's always a copy wherever I go!!