Summa Theologiae

⚖The case for it

The most ambitious intellectual construction of the Middle Ages. Aquinas synthesizes Aristotle, Augustine, and Christian theology into a systematic whole. The Five Ways (proofs of God's existence), natural law theory, and the treatise on happiness remain live arguments. Even if you're not Catholic or not religious, the Summa is a masterclass in organizing thought. Aquinas considers every objection before answering. More philosophers should try that.

— the canon

✕The case against

Aquinas never finished it; he stopped writing after a vision and called everything he'd done straw. What exists runs well past a million words in a format (objections, sed contra, reply to each) that never once varies across thousands of articles. The metaphysics presumes Aristotle's physics. You can admire the cathedral and still notice that nobody reads it whole; even Dominicans use the index.

— the honest librarian