distinct from one another; in their own terminology they are two substances. If, then, those two substances turn into one single substance instead of remaining two, it necessarily follows that this third entity is neither pure God nor pure man, nor is it the two distinct substances of divinity and humanity—for the latter would still be two substances, not one. Rather, it becomes a third thing, blended, intermingled, and transmuted from both, so that the very reality of the Godhead and the very reality of manhood are altered, and this third substance—being neither unmixed divinity nor unmixed humanity—takes on the same character as every other form of union that is known.

Whenever two things unite and become one substance, some transmutation is inevitable, as we observe when water joins with milk, with wine, or with anything else that mixes with water. By contrast, water and oil remain two separate substances just as they were; the oil merely clings to the water and floats on its surface without actually uniting with it. The same holds for the mingling of fire with iron: the iron is transformed from its former state, and when it cools it returns to what it was. Likewise, when air unites with water and earth it becomes vapor or dust and the like.

In short, in every instance of union known to people, once the two become one and duality disappears, the alteration of both parties is unavoidable.

Should someone object, “Within him are the two natures and the two wills, just as in the mixture of water and milk there remain the powers of water and the powers of milk,” we reply: even so, each of those powers must inevitably be modified from what it originally was.