so that we call a thing wet when wetness has the larger share in it, and dry when dryness does; and in the same way hot when the hot in it prevails over the cold, and cold when the cold prevails over the hot. That, then, is how the names are used.

Two new nouns appear, hygrotēs, "wetness," and xērotēs, "dryness." They are the qualities as abstract amounts, which is what a mixture is made of. The chapter ends on a plain definition, and it is the one Western medicine used for the next fifteen hundred years. When a medieval herbal calls pepper "hot" or lettuce "cold," it is using Galen’s rule from this page: the name tells you which quality wins.