In recognizing that consciousness, the nature of understanding, the mental activity in its general form, consists in developing general concepts out of concrete objects, we circumscribe this insight by stating that reason develops its understanding out of contradictions. It is the nature of the mind to perceive, in given phenomena of different dimensions and different duration, the nature of things by their semblance, and their semblance by their nature; to distinguish in wants of various degrees the most essential and necessary from the less pressing; to measure within a certain circle of magnitudes the large by the small and the small by the large, or in other words to compare the contrasts of the world with one another, to harmonize them by explanation. Common parlance instinctively calls understanding judging; judging requires a certain standard. Just as surely as we cannot perceive any objects which are "in themselves" great or small, hard or soft, clear or dark, just as surely as these terms denote certain relations and require a certain standard by which their relations can be determined, even so does reason require a certain standard for the determination of that which is reasonable. The fact that we consider certain actions, institutions, conceptions, maxims of other periods, nations, or persons unreasonable is simply due to the application of a different standard, because we ignore the premises, the conditions, which cause another's reason to differ from our own. Men who differ in their mental estimates, in their understanding of things, may be likened to the thermometers of Reaumur and Celsius, one of which designates the boiling point by 80 and the other by 100. A different standard is the cause of this different result. On the so-called moral field there is no scientific agreement, such as we enjoy in some physical matters, because we lack the uniform standard which natural science has long since found. It is still attempted to perceive the reasonable, good, right, etc., without empirical data, by speculative reasoning without experience. Speculation seeks the cause of all causes, the immeasurable cause; truth "itself," the unconditional and standardless truth; the unlimited good, the unboundedly reasonable, etc. The absence of a standard is the essence of speculation, and its practice is characterized by unlimited inconsistency and disagreement. If there are followers of certain positive religions who agree in the matter of morals, they owe this to the positive standard which certain dogmas, doctrines and commandments have given them. But if any one tries to perceive things by "pure" reason, the dependence of this reason on some standard will be demonstrated by its "impure," that is to say individual, perceptions.