Philosophia perennis (Aristotle, Aquinas & Co.) takes on all comers (from Hobbes to Wittgenstein and most major names in between) and knocks them all out--as usual in Adler's argumentative bouts. Locke and his followers think all ideas are what we apprehend through consciousness; they ignore ""cognitive ideas,"" or the means of apprehending whatever we are conscious of. This leads us into materialism and subjectivity. Locke, Hume, and Berkeley identify the mind with sense, thereby trapping it in the limited field of sense-perceptions, denigrating conceptual knowledge, and paving the way for nominalism. Hobbes and the 20th-century linguistic philosophers who are his heirs reject all talk of ""incorporeal substance"" as meaningless--there go the angels and God, even as mere subjects of discourse. Kant makes the disastrous error of abandoning traditional metaphysics and declaring the real to be unknowable. The Kantian seed sprouts in the work of positivists like Karl Popper who claim that empirical falsifiability is the only test of true knowledge. Ayer and the prescriptivists hold that ethics has no cognitive status because nothing can bridge the gap between ""is"" and ""ought""--forgetting that matters of fact and prescriptive judgments can be linked by the self-evident axiom grounding all moral philosophy: ""We ought to desire whatever is really good for us and nothing else."" As this supposed ""first principle"" suggests, Adler grossly oversimplifies. He also does scant justice to his opponents (who, even if one assumes they were mostly wrong, have illuminated our experience). Adler retains well-honed pedagogical skills: he's clear, logical, nontechnical And, of course, anyone defending epistemological realism, free will, a unitary human nature, or Aristotelean ethics has a distinct advantage in taking what seems to be the common sense position. Philosophical novices can learn a good deal from this brisk polemical survey, but they should be warned that it's not a fair fight.