In contemporary discussions of abortion, both sides argue well-worn positions, particularly concerning the question, When does human life begin? Though often invoked by the Catholic Church for support, Thomas Aquinas in fact held that human life begins after conception, not at the moment of union. But his overall thinking on questions of how humans come into being, and cease to be, is more subtle than either side in this polarized debate imagines. Fabrizio Amerini--an internationally renowned scholar of medieval philosophy--does justice to Aquinas's views on these controversial...