To exemplify the point that any techne deals with the whole of the field of that techne, Socrates refers to graphike techne, meaning here just painting. Socrates proceeds, however, to talk about the critic of one artist needing to be able to criticize all artists if indeed the techne pertains to the whole. Earlier, Io had said that he excelled as a critic of Homer, but not of other poets, so Socrates' analogy is accurate, although it does not prove the point about techne pertaining to the whole of its field.
