Throughout the history of western Christianity, a major stumbling block has been agreement upon the definition of certain terms. Milton and his critics have shared in the difficulty of communication which lack of a common terminology has caused. Nowhere is this more evident than in his discussion of the Son of God in the Christian Doctrine, where his employment of “substance,” “subsistence,” “essence,” and “hypostasis” has confused students who were attempting to understand the complex meanings which lie back of these words. Milton has often not followed the interpretations of these words usually held in Christianity; rather, he has adopted meanings which were very early associated with them but which lost currency centuries ago, even though they have never been completely forgotten.