Paul Tillich (1886–1965) was born and raised in Germany. He received his PhD in 1910 and in 1912 was ordained in the ministry. From 1914 to 1918 he served as a chaplain in the First World War. Returning from the war, he taught both philosophy and theology at several universities. In 1933 the Nazi government suspended Tillich's position at the University of Frankfurt. He then went to the United States where, until 1937, he was Visiting Professor of Philosophy of Religion and Systematic Theology at Union Theological Seminary. He served at Union as Associate Professor of Philosophical Theology (1937–40) and Professor (1941–55). From 1955 to 1962, he was a University Professor at Harvard, and during his last three years he was the Nuveen Professor of Theology in the Divinity School of the University of Chicago. He was buried in New Harmony, Indiana. Tillich wrote a number of books among which are the following: Systematic Theology (3 vols, 1951–63), The Courage to Be (1952), Biblical Religion and the Search for Ultimate Reality (1955) and Dynamics of Faith (1957).

In his writings Tillich describes certain basic questions (he calls them ‘existential questions’) that arise out of the human situation. These questions cannot be answered within that situation. Their answers, he claims, are found in the great symbols of the Christian message. In his writings he endeavours to analyse the human situation and to interpret the traditional Christian symbols as answers to this situation.

It is fitting that one of the last pieces of philosophical writing to come from Reid's hand should bear the title “Of Power.” For the concept “power” lies at the foundation of Reid's account of agent-causation, which in turn is the central idea in his account of human freedom and responsibility. In this final piece of philosophizing on this subject, Reid begins by pointing out that: “Every voluntary exertion to produce an event implies a conception of the event, and some belief or hope that the exertion will be followed by it” (OP: 3). Accordingly, our willing (deciding) to take a walk in the woods implies our having a conception of our taking a walk in the woods and some belief or hope that an exertion of ours intended to bring that about will be followed by our taking a walk in the woods. Reid takes this claim of his to imply that a conception of power is antecedent to every deliberate act.

Does he think that the earliest exertions by an infant involve a conception of power? No. Reid thinks that our earliest exertions are instinctive, unaccompanied by a conception of some goal to be accomplished. It is only when experience teaches us that certain exertions are followed by certain events that we learn to make these exertions voluntarily and deliberately in order to produce such an event. And once we believe that the event depends upon our exertion, we then have “the conception of power in ourselves to produce the event” (ibid.). Reid therefore concludes that our conception of power “is the fruit of experience and not innate” (ibid.).