II. The true and proper history of the practical principle, conceived as autonomous, and of the problem concerning the identity or the distinction of the practical from theory, has a different line of development. As a rule this problem is referred back to the celebrated sayings of Socrates, that virtue is knowledge and vice ignorance, and to the corrections that Aristotle, while accepting, proposes in them, when he takes note of the part that belongs to the non-cognoscitive element. But, as often happens, those sayings and those corrections have been taken as being more profound than they genuinely were and could be. This, if it have not aided the exactness of historical interpretation, has nevertheless stimulated and fecundated thought. On reading without prejudice the parts of the _Memorabilia,_ of the Platonic dialogues, of the _Nicomachean Ethics,_ and of the _Magna Moralia_ that relate to it, it appears evident that what is treated of in them is the altogether empirical question of the importance that mental development has for practical life, and whether knowledge suffices for this, or natural dispositions and discipline of the passions be not also necessary. Aristotle replied to Socrates, who had insisted upon the element of knowing, conceiving virtue as knowledge (λόγος), by modifying the statement with the assertion that virtue is not indeed simply knowledge, but is _with_ knowledge (μετὰ λόγου). In these very ingenuous considerations is to be found at the most implicitly, but certainly not explicitly, the problem that was only stated later on; and it would be rash to classify Socrates as an intellectualist and Aristotle as a voluntarist. It is certain that the Aristotelian philosophy, in accordance with good sense, preserved the distinction between the two forms of the spirit, the theoretical and the practical, the reason and the will, a distinction that has also passed into the scholastic philosophy (_ratio cognoscibilis, ratio appetibilis_) and into that of the Renaissance. But it remained always vague, sometimes brought into prominence, sometimes, on the other hand, attenuated. Almost dissipated in those who conceive the principles of the practical as something similar or analogous to mathematical truths (Cudworth, Clarke, Wollaston, etc.), it always reaffirms itself when importance is given to the affections and passions, as is the case with many thinkers of the seventeenth century (Bacon, Descartes, Spinoza, Vico); and the doctrines of the Scottish school of sensationalists contributed not a little to keep it alive.