And yet, after we have denied the logical existence of error, we are still confronted with the mass of positive errors which we can more or less easily identify in the course of history and in our daily experience. Positive errors, that is, affirmations of knowing that which we do not know, are real products of our activity: but since the theoretical value, truth, is absent from them, they cannot be products of the theoretical activity. They must therefore be products of the only other form of spiritual activity, the practical. Ignorance or obscurity or doubt are not errors; they are the inexhaustible matter to which the spirit of man is perpetually giving form and reality. To be aware of one's ignorance is in fact the first stage in the research of truth, the _initìum sapientæ_. Thought and truth are affirmation; the positive error is an affirmation also, which simulates truth. We cannot think an error, but we can pass from thought to action, by making a false affirmation, a purely practical affirmation, which consists in the act of producing sounds to which no thought corresponds, or, which amounts to the same, only a thought without value, without coherence, without truth. What we have qualified in its negative aspect as a theoretical error manifests itself in its positive aspect as an act of will, directed to a certain end, a practical act, and, as such, having its own rationality, which is neither logical, nor moral, but purely economic, consisting in the adequacy of that particular affirmation to the individual purpose by which it has been prompted. Morality requires that the thinking spirit should realize itself as truth; and therefore the economic act which is error, though logically unreal, though economically useful, finds inevitably its ultimate sanction in a moral condemnation.