Yet the value of knowledge is not justified purely in pragmatic terms. In Prop. Plac., Galen puts forward a more subtle, tripartite division of areas of knowledge: (1) matters on which he claims that it is possible to have, and that he has, certain knowledge; (2) matters on which he claims no knowledge; and (3) matters on which he claims only to be able to advance to the “plausible”, but where the attempt to gain knowledge is still worthwhile, even though they are not of direct practical value (Prop. Plac. 14, 114–17). This last category is in a sense the most interesting and Galenically distinctive. Such knowledge, he suggests, “would adorn the art, if knowledge could be obtained”; he seems here to associate this category with element theory. If so, this acknowledgement of a limitation on certainty will affect our view of Galen’s “demonstrations” in this area (§3.1 above). Perhaps, although it is not apparent from his dedicated—and highly polemical—discussions in Hipp. Elem. and in HNH, this is after all an area where he admits to something less than scientific certainty, at least in detail.