Aquinas was a 13th century university teacher educating students in an ecclesiastical tradition, but because he thought authority without reason could not make sense of truth he taught questioning. Timothy McDermott examines some of Aquinas's questions and asks whether they can make sense of the truths the 21st century takes for granted. He considers the role of regularity and chance in the natural world, mind and matter, freedom and moral obligation, law and society, suffering and evil, hope and hopelessness, and what place can rationally be given to Jesus Christ, to religion and churches, to faith and love and a God. Extracts are taken from the records of Aquinas's classroom disputations (Quaestiones Disputatae) and two brilliant conspect uses of his teacher: the Summa Contra Gentes attempting a reasoned dialogue with non-Christian (mainly Arabic) scholars, and the Summa Theologiae addressed to his Christian students.