The leading contradiction which is corrected in the "Agnoiology or Theory of Ignorance" claims that there can be an ignorance of that of which there can be no knowledge. It is corrected by appealing to the fact that Ignorance is a defect, and argues that there is no defect in not knowing what cannot be known by any intelligence (for example, that two and two make five), and therefore there can be an ignorance only of that of which there can be a knowledge, that is, of some-object-plus-some-subject. Therefore, the knowable alone is the ignorable. Ferrier lays special claim to originality for this division of the Institutes.