A thought and its privative alone--that is, a quality and its negative--cannot lead to a more comprehensive thought. It is devoid of relation and barren. In pure logic this is always the case, and must be so. In concrete thought it may be otherwise. There are certain propositions in which the negative is a reciprocal quality, quite as positive as that which it is set over against. The members of such a proposition are what are called “true contraries.” To whatever they apply as qualities, they leave no middle ground. If a thing is not one of them, it is the other. There is no third possibility. An object is either red or not red; if not red, it may be one of many colors. But if we say that all laws are either concrete or abstract, then we know that a law not concrete has all the properties of one which is abstract. We must examine, then, this third law of thought in its applied forms in order to understand its correct use. It will be observed that there is an assumption of space or time in many propositions having the form of the excluded middle. They are only true under given conditions. “All gold is fusible or not,” means that some is fusible at the time. If all gold be already fused, it does not hold good. This distinction was noted by Kant in his discrimination between _synthetic_ judgments, which assume other conditions; and _analytic_ judgments, which look only at the members of the proposition. Only the latter satisfy the formal law, for the proposition must not look outside of itself for its completion. Most analytic propositions cannot extend our knowledge beyond their immediate statement. If A is either B or not B, and it is shown not to be B, it is left uncertain what A may be. The class of propositions referred to do more than this, inasmuch as they present alternative conceptions, mutually exhaustive, each the privative of the other. Of these two contraries, the one always evokes the other; neither can be thought except in relation to the other. They do not arise from the dichotomic process of classification, but from the polar relations of things. Their relation is not in the mind but in themselves, a real externality. The distinction between such as spring from the former and the latter is the most important question in philosophy. To illustrate by examples, we familiarly speak of heat and cold, and to say a body is not hot is as much as to say it is cold. But every physicist knows that cold is merely a diminution of heat, not a distinct form of force. The absolute zero may be reached by the abstraction of all heat, and then the cold cannot increase. So, life and death are not true contraries, for the latter is not anything real but a mere privative, a quantitative diminution of the former, growing less to an absolute zero where it is wholly lost.