If you are interested in the science behind casting spells, why too much and too little sex is not good for your life, and whether it is possible to predict future from dreams or speculate while asleep, this book is for you. We present the first complete critical edition of the set of commentaries on Aristotle's short psychological and physiological treatises, the so-called Parva Naturalia, penned by Walter Burley, an early fourteenth century Oxford philosopher, later William of Ockham's most formidable opponent. It is a true compendium of medieval natural philosophy, putting together information taken from Aristotle, Avicenna, Averroes, Albert the Great, Thomas Aquinas, Peter of Auvergne, Simon of Faversham, and many more.