Criticism (an anthology of literary criticism from the early 1950's).
I was introduced to this deceptively simply titled book as an undergraduated and have never lost track of my copy (there is a similar modern volume The Norton Anthology of Literary Criticism). It might be considered cheating to select an anthology, but two of the works, Aristotle's Poetics and Horace's Ars Poetica have been seminal to nearly all western literature since they were written. My argument is simple: everyone thinks and every thinking person can benefit from some advice and guidance on how to frame those thoughts in the interest of communication with their fellow thinkers. If, therefore, Aristotle and Horace's essays underly nearly all western writing for the last 2.5 millenia (either by authors who agree or disagree with their many premises), given the sudden destruction of all books but one, they would just as easily generate a whole new library of human thought, both as entertainment and instruction and very possibly, on their second attempt, help to safe us from ourselves.
John-Michael Albert, poet