"We must therefore completely resolve and separate Nature, not by fire, certainly, but by the mind, which is a kind of divine fire. Therefore the first task of true induction (as far as discovering forms is concerned) is the rejection or exclusion of all the separate natures that are not found in any instance where the given nature is present, or are found in any instance when the given nature is absent, or are found to increase in any instance when the given nature decreases, or to decrease when the given nature increases. Then indeed, after the rejection and exclusion have been properly made, in the second place (at the bottom, as it were), there will remain, all volatile opinions vanishing into smoke, the affirmative form, solid, true, and well- defined. Now this is quickly said, but it is only reached after many twists and turns."