If there were an option to give this book four and a half stars, I would. As that option's not available, I've chosen to round up rather than down. There are simply too many thought-provoking, musically relevant (if you like Sabbath) and generally clever observations peppered throughout the book for it to be rounded down to a four. Why not a definitive, no-hesitation five? Because, as is the case with most philosophical writings, pretentiousness makes frequent appearances, sometimes accompanied by outright preposterousness. This is not always a bad thing. Usually it's irritating but at times it can be amusing.
By far the most enjoyable parts of the book come when a particular writer (each of the book's chapters is written by a different author) gets deliberately light-hearted whilst applying recognised philosophical themes to specifics of Black Sabbath's music, lyrics, artwork, image or band members. The best example of this is the entirety of chapter 7 - The Art of Black Sabbath - which is written by Professor of Philosophy Greg Littmann. More than any of the book's other chapters (all of which I enjoyed), this one had me in stitches. Littmann writes it like some parallel-Universe literary version of Bill and Ted's Excellent Adventure, with Aristotle auditioning for Black Sabbath in the 1960s, desperate to be accepted into the band, and going to great lengths to convince Ozzy, Tony, Geezer and Bill of why they should accept him into the fold. Genius is an overused word, but this chapter is proper genius. It's also comedy gold.
I won't pontificate about other chapters. Doing so would give away some surprises and thereby prevent them from being surprises if/when this review's readers go on to read the book. So my revelations would be sort of paradoxical spoilers - slayers of surprises. I don't want to be that guy, so instead I'll do something useful by summing up who might enjoy Black Sabbath and Philosophy: Mastering Reality.
If you're a fan of Black Sabbath but don't have any particular interest in philosophy, there's a good chance you'll enjoy the book and have some laughs along the way.
If you're a fan of philosophy but don't have any interest in Black Sabbath, the book will be anathema to you, as the songs/lyrics/tours/events/musicians mentioned will have no meaning to you, and therefore no resonance within you.
If you're a fan of Black Sabbath and a philosophy enthusiast (as I am), this book is custom-made for you. It will be entirely your cup o' tea.
If you don't like Black Sabbath and you think philosophy's a pile of old shite, this book is definitely not for you. But you don't need me to tell you that.