Joseph Bobik offers a translation of Aquinas's (circa 1252) and (1273) accompanied by a continuous commentary, followed by two essays: "Elements in the Composition of Physical Substances" and "The Elements in Aquinas and the Elements Today." introduces the reader to the basic Aristotelian principles such as matter and form, the four causes so fundamental to Aquinas's philosophy. examines the question of how the four elements (earth, air, fire, and water) remain within the physical things composed from them.