The Metaphysical Foundations of Love: Aquinas on Participation, Unity, and Union offers a systematic treatment of St. Thomas Aquinas’s account of the metaphysical relations of unity-to-union and unity-to-participation in God as the key structuring elements to the nature of love and friendship. In general, Aquinas identifies love as the source and summit of the life of each human being. Everything in the created realm issues forth from God’s creative love, and the ultimate end of all human persons is the greatest possible union with God. Aquinas contends that the love of friendship allows for the greatest union between two persons; thus, the greatest union with God takes the form of friendship with him.