Falsity and Difference

In the Sophist, Plato at one point illustrates difference as a fundamental component of the method of division through which language organizes reality. Later, he explains falsity in terms of difference, so that to make a false statement is to state something different from what is true. Taken together, these two examinations seem to suggest that falsity is a necessary component of language. This seems to resonate with a statement in Williams'  introduction to the Theaetetus that both the Theaetetus and the Sophist deal with the "radical discovery... that knowledge is necessary for error" (p. xvii). This seems to make sense especially if the theory of forms that we are dealing with is largely an attempt to explain how knowledge can be possible.