Assesses Aristotle’s influence in early Islam and late medieval Europe. The philosopher’s works thrive in confident historical eras: to know is to understand causes; to reason is to press boundaries. Aristotelian thought fell into desuetude with the fall of the Roman empire; traveled to Persia and Mesopotamia in the 6^th century with the flight of Nestorius; and spurred Averroes, Avicenna, and Maimonides who elaborated the connection of reason and Muslim faith. They  were surpassed in the 12^th century by al Ghazali, who contended that God produces all effects. Still Muslim advances into Europe brought Aristotle back to the Latin world, where Dominicans in particular saw reason as elaborating faith, none more than Thomas Aquinas. The doctrinal controversies of the next three centuries turned on where to draw boundaries; the neoplatonic division of spirit and matter was sidelined. Aquinas’ dual causation asserted God causes matter to cause themselves. William of Ockham initiated the Western sundering of faith and reason, by asserting it was too complicated to coexistence, paving the way for Luther to complete the split (albeit more on a socioeconomic basis). The idea of medieval dark age is dependent on the prejudice that science had to free itself of fundamentalism; conversely fundamentalist doctrine too emerged from (i.e., did not preexist) the attack of Aquinas’ absolution of Aristotelian science. Lively and told in a light, almost smarmy, manner but dated in failing to confront Aristotle’s postmodern challengers.