P27: We know nothing to be certainly good or evil, except what really leads to understanding or what can prevent us from understanding.

Dem.: Insofar as the Mind reasons, it wants nothing other than to understand, nor does it judge anything else to be useful to itself except what leads to understanding (by P26). But the Mind (by IIP41, P43, {II/228} and P43 S) has certainty of things only insofar as it has adequate ideas, or (what is the same thing, by IIP40 S)16 insofar as it reasons. Therefore, we know nothing to be certainly good except what really leads to understanding, and conversely, know nothing to be certainly evil except what can prevent us from understanding, q.e.d.