Falsity consists in the privation of knowledge, which inadequate, fragmentary, or confused ideas involve.
Proof .-- There is nothing positive in ideas, which causes them to be called false (II.

xxxiii.); but falsity cannot consist in simple privation (for minds, not bodies, are said to err and to be mistaken), neither can it consist in absolute ignorance, for ignorance and error are not identical; wherefore it consists in the privation of knowledge, which inadequate, fragmentary, or confused ideas involve.

Q.E.D.
Note .-- In the note to II.xvii.I explained how error consists in the privation of knowledge, but in order to throw more light on the subject I will give an example.

For instance, men are mistaken in thinking themselves free; their opinion is made up of consciousness of their own actions, and ignorance of the causes by which they are conditioned.

Their idea of freedom, therefore, is simply their ignorance of any cause for their actions.