Bob Dylan doesn’t think much of the current state of songwriting or of contemporary pop music, two points underscored in his sometimes dizzying, sometimes confounding, but rarely less than absorbing new book, “The Philosophy of Modern Song.” But he does think polygamist marriages are greatly underrated, about which more in a moment. Twelve years in the making, Dylan’s book — which will be published Tuesday by Simon & Schuster — is largely an impassioned valentine to dozens of the great songwriters and singers most admired by one of the greatest singer-songwriters extant. They range from Hank W…
