Calvin began his study of the doctrine of the Sacrament of the Holy Supper independently of both Luther and Zwingli. His position as the theologian of Switzerland, and his friendship with his colleague William Farel, who was a Zwinglian, made him adapt his theory to Zwinglian language; but he borrowed nothing from the Reformer of Zurich. He was quite willing to accept Zwingli's exegesis so far as the words went; but he gave another and altogether different meaning to Zwingli's phrase, _This signifies My Body_. He was willing to call the "elements" _signs_ of the Body and Blood of the Lord; but while Zwingli called them signs which _represent_ (_signa representativa_) what was _absent_, Calvin insisted on calling them signs which _exhibit_ (_signa exhibitiva_) what was _present_--a distinction which is continually forgotten in describing his relation to the theories of Zwingli, and one which enabled him to convince Luther that he held that there was a Real Presence of Christ's Body in the Sacrament of the Holy Supper. To describe minutely Calvin's doctrine of the Holy Supper would require more space than can be given here, and a brief statement of the central thoughts is alone possible. His aim in common with all the Reformers was to construct a doctrine of the Sacrament of the Supper which would be at once scriptural, free from superstition and from the crass materialist associations which had gathered round the theory of transubstantiation, and which would clearly conserve the great Reformation proclamation of the spiritual priesthood of all believers. He went back to the mediæval idea of transubstantiation, and asked whether it gave a true conception of what was meant by _substance_. He decided that it did not, and believed that the root thought in _substance_ was not dimensions in space, but power. The _substance_ of a body consists in its _power_, active and passive, and the _presence_ of the _substance_ of anything consists in the immediate application of that power.[40] When Luther and Zwingli had spoken of the _substance_ of the Body of Christ, they had always in their mind the thought of something extended in space; and the one affirmed while the other denied that this Body of Christ, something extended in space, could be and was present in the Sacrament of the Supper. Calvin's conception of _substance_ enabled him to say that wherever anything acts there it is. He denied the crude "substantial" presence which Luther insisted on; and in this he sided with Zwingli. But he affirmed a real because active presence, and in this he sided with Luther.