Brian Massumi is probably best known for his translation of Deleuze and Guattari's A Thousand Plateaus, along with his excellent "reader's guide" he published on the subject. Since then Massumi has only released a few full-length books, and this is his most recent.
Deleuze is still a major reference for Massumi, but he shares equal footing with William James and Alfred North Whitehead in this book, along with Walter Benjamin and Charles Pierce in some later chapters. This book is primarily about ontology and aesthetics. Massumi, at base, wants to understand the underlying aspects of art (and by virtue of art, experience in general) and how it can be political. He spends a lot of time musing on the abstract character of perception, what he at times calls "semblance" and other times terms "lived abstraction" (the terms are related but not synonymous) but always takes his starting point to be actual events. This means that specific artists and art pieces are brought up and discussed at length; these are generally visual pieces but there is also a rather illuminating discussion of Mahler in one of the later passages. In this way, what would otherwise be obtuse constructions (like "Every event is a qualitative-relational economy of process, 'full of both oneness and manyness'") if not immediately explained, is illustrated very well by the time the book is finished.
Massumi takes James's "radical empiricism" seriously, and he terms his appropriation of it "speculative pragmatism." What this generally means is to take the abstract qualities (modes of perception, "virtual" aspects of perception, the ways of interaction with something) of processes or events and construct a philosophy (what Massumi calls an "activist philosophy") which is rooted in perception but is able to describe the abstract undercurrents of these seemingly mundane, singular events. In this way, art (and events of experience in general) can be considered in the way in which they shape relation between different things, As Massumi writes: "The relational-qualitative duplicity at the heart of activist philosophy is a differential, not a dichotomy. It concerns coincident differences in manner of activity between which things happen. The coming-together of the differences as such--with no equalization or erasure of their differential-- constitutes a formative force...Between them, they co-compose a singular effect of unity resulting from how it is that they come differently together. An integral of action and experience--a dynamic unity of self-enjoying occurrence--emerges from the energetic playing out of their impulsive difference." For those familiar with Deleuze, the word "affect" is really is significant here. From here, Massumi goes in many directions, but they all seem connected by this notion.
This book is not an especially easy read. For those who have read Massumi's work before, you know what to expect. For those who may only be familiar with some continental philosophy it should be noted that, while Massumi's style is not typical of some less-than-clear writers in the tradition (Derrida, Deleuze, Lacan are examples; these folks are great, but they are tough to read) it is sometimes a bit rough-going. His sentences can be complex, and he will often hyphenate two words to give them each a very specific meaning (see above). This does not happen for the entire book, but it is present throughout. In general, I found it to be easy to figure out what he was talking about but it meant I had to read slower than usual. By the end of the book I found myself appreciating the way Massumi expressed his ideas, it just took some getting used to.
I have also read works by Deleuze, Guattari, and a few authors theoretically close to Massumi so I have some experience with these kinds of concepts. I mention this because I am unsure how easy it would be for someone with no prior experience with these philosophers' ideas to get the most out of this volume.
Overall, I enjoyed this book,I learned a lot from it and would recommend it to people who are interested and willing to invest the time. If there is an aspect of the book that you would like to know more about, feel free to comment and I will hopefully be able to respond or edit this review .