Observation is the only means of bringing back one who has thus strayed away; such a one has departed from reason, and cannot be brought back to it by means of reason. Observations directed to him must be more of a call, a sort of alarm to arouse reason, not a combination to re-construct it: he is as a man asleep, or one in a swoon, and we must call him, and shake him, in order to arouse him; we must not dispute with him as with an adversary.(19) CHAPTER XX. TRUE SENSE OF THE PRINCIPLE OF CONTRADICTION.--KANT'S OPINION. 189. Before examining the value of the principle of contradiction as a basis for our cognitions, it will be well to fix its true and exact sense. This renders necessary some considerations upon an opinion of Kant, advanced in his _Critic of Pure Reason_, when treating of the form in which the principle of contradiction has hitherto been enunciated in all schools of philosophy. The German metaphysician grants, that whatever may be the matter of our cognitions, and in whatever manner they may relate to their object, it is a general, although a purely negative, condition of all our judgments, that they should not mutually contradict each other; otherwise, even without reference to their object, they are nothing in themselves. This doctrine established, he observes that what is called the principle of contradiction is the following: "A predicate that is opposed to a subject does not belong to it;" and then goes on to say, that this is a universal, although purely negative criterion of all truth; that it moreover belongs exclusively to logic, since it is of use to pure cognitions as to cognitions in general, without relation to their object, and he declares that the contradiction makes them completely disappear. "But of this celebrated principle, although stripped of all contents, and purely formal," he continues, "there is still a formula containing a synthesis, which has inadvertently, and quite unnecessarily, been mixed up therein. It is this: _It is impossible for the same thing to be and not be at the same time._ Not only has the apodictic certainty (by the word _impossible_) been unnecessarily added, which certainty would have been of itself understood from the proposition; but the proposition is affected by the condition of time, and says, as it were: a thing = A, which is something = B, cannot at the same time be not B, but it can very well be both (B as well as not B) in succession. For example: a man who is young, cannot at the same time be old; but the same person may very well be young at one time, at another not young, that is, old. Now, the principle of contradiction, as a mere logical principle, must not at all restrict its meaning to the relations of time, and consequently, such a formula is quite opposed to its intention. The misapprehension arises simply from this: that we first separate the predicate of a thing from its conception, and afterwards unite its opposite with this predicate, which never