 In the introduction to his Principles of Human Knowledge (1710, section 16), Berkeley reiterates 13 centuries later Proclus’s take on the generality problem. Though one always has a particular triangle ‘in view’ when working through a demonstration about triangles, there is ‘not the least mention’ of the particular details of the particular triangle in the demonstration. The demonstration thus proves, according to Berkeley, a general proposition about triangles. 