Abstract
The purpose of this work is to summarize and clarify a centrally important but often neglected theme in the writings of Aquinas. The reason for the neglect, and the justification for presenting the work, lie in the difficulty, even for constant readers of Aquinas, of grasping this complex theme as a whole: on the one hand the texts which explicitly treat of it are widely scattered throughout Aquinas's writings, while on the other hand it may be said to be implicitly present nearly everywhere in his work. The success of the present volume, then, must be measured by the extent to which fidelity to the many texts and to Aquinas's overall intention is combined with a clear and orderly presentation.