LOCKE 761
knowledge is not entitled to be called "knowledge," and that it is merely presumption more or less probable. Instead of the immediate or the demonstrable insight, which alone is what he intends by knowledge, it is only "assent," "opinion," "probability."
Locke's report about human knowledge and the narrow extent of it is contained in the first thirteen chapters of the fourth book. The remainder of the book is concerned for the most part with what he found when he examined instances of "assent" or reason able presumption, so liable to error, but on which human life really turns, as he and Butler are fond of reminding all transcendentalists. He takes for granted that "all the knowledge we have or are capable of" must be discernment of one or other of four sorts of agreement or disagreement among our thoughts themselves, or between our individual thoughts and the reality that is inde pendent of them. All that can be conceivably known must be either (a) relations of identity and difference in what we are conscious of, that, for instance, "blue is not yellow"; or (b) this thought being mathematically related to that, as, for instance, that "two triangles upon equal bases between two parallels must be equal"; or (c) that one quality does or does not coexist with another in the same substance, as that "iron is susceptible of magnetical impressions"; or (d) that a thought has a real objective existence, independent of our individual mind, as that "God exists," or the "earth exists." What would now be called merely analytical know ledge exemplifies the first sort; mathematical (Locke would add moral) knowledge represents the second; physical and natural science, if this can become knowledge proper at all, -would come under the third head; metaphysical knowledge forms the fourth. The third and several following chapters of this concluding book of the Essay are really an inquiry, under these four heads, how far knowledge is possible for man in mathematics, and in morality; about nature or natural phenomena in relations of coexistence and succession; and about the hyperphenomenal reality of our own existence, the existence of God, and the existence of matter. Locke found a difference among the examples of what "knowledge" is that were offered in his natural experience. In some instances the known relation was at once evident, as when he judged that a circle was not a triangle, or three more than two and equal to one and two. In other cases the known relation was perceived only through the medium of something else, as in a mathematical con clusion, in which each step is taken by a rational intuition. The former is rationally intuited and the latter rationally demonstrated knowledge. In strictness all knowledge or rational certainty, he would have it, is in one or other of these two kinds. There is, however, a third sort of certainty which rather puzzled him. He found that "our perceptions of the particular existence of finite beings without us" go beyond mere probability, although they are not examples of rational necessity. There is nothing contradictory to reason in the supposition that our sense-perceptions are illusory, although we are, in fact, incapable of doubting their reality. We find ourselves "inwardly conscious of a different sort of percep tion," when we look on the sun by day and only imagine the sun at night. This, which is Locke's third sort of knowledge, might be called sense-perception. The difficulty that a "sense-perception" only of the present moment, divorced from the past and the future, can be other than "blind," or irrational, does not occur to him.
Locke next inquired to what extent a human knowledge – in the way either of intuitive or demonstrative rationality, or of sense perception – is possible in regard to each of the four*(already mentioned) sorts of knowable relation in which must be contained all knowledge we can be supposed capable of. Our knowledge must of course be confined within our "ideas"; for it is self-evident that we cannot have knowledge of a thing if consciousness is dormant. But there is only one of the four sorts of knowable relation in regard to which our knowledge is coextensive with our thoughts. The only knowable relation which he finds to be coextensive with his thoughts is that of "identity and diversity"; we cannot be conscious at all without distinguishing, and every affirmation implies negation. The second sort of knowable relation – purely rational concatenation among our thoughts – is intuitively and also demonstrably discernible in thoughts about quantities, in forms of space, time, and number; it is through this discernment that the mathematical sciences are constructed. Morality too, Locke thinks, as well as quantity, is capable of being thus rationalized. "Where there is no property there is no injustice," he offers as an example of a proposition "as certain as any demonstration in Euclid." Only we are more apt to be biassed, and thus to have reason withdrawn from us, in dealing with problems of morality than in dealing with those of mathematics. Mankind might in consequence, in questions of morals, "with Egyptian darkness expect Egyptian bondage, were not the candle of the Lord set up by himself in their minds" (ch. 4, § 20). It is not easy to say whether the mathematics and morality which Locke finds thus demonstrable would be, as understood by him, sciences of what Kantists call analytical judgments founded on arbitrary definitions, or sciences consisting of synthetical judgments a priori.
In turning from mathematical and moral relations to those of
coexistence and succession among phenomena, – Locke's third sort of knowable relation, – he finds the light of pure reason disap pear, although the relations in question are those in which "the greatest and most important part of what we desire to know" consists. Of relations of this third kind, with which all the physical and natural sciences are concerned, he reports that "our knowledge is very short, if indeed we have any at all," and are not wholly thrown on presumptions of greater or less probability, or even left in ignorance. According to the philosophy of the Essay "there can be no science of bodies." All physical and natural science depends on a knowledge of the relations between the secondary qualities and other powers of bodies on the one hand, and the primary or mathematical qualities of their atoms on the other, or else "on something yet more remote from our compre hension." Now, as a rational insight of these relations, either in tuitively or through demonstration, is beyond our reach, we must be satisfied with inductive presumptions, which the completest "verification" leaves, after all, only presumptions that more facts might prove to be unwarranted. Our inductive generalizations about particular things must always involve an element of possible error, or at least inadequacy, and therefore of probability only. Arbitrariness of connexion, and not rational necessity, reigns over the whole realm of physical government, with its relations of constant coexistence and succession; we only presume, as reasonably as we can, what its actually established laws are, and we can only presume that these laws are sustained in a steady and uniform government. The presumption is "sufficient for our purposes."
The amount of our knowledge under Locke's fourth category of knowable relations – those of real metaphysical or metaphenomenal existence – is reduced, in his report, to – (a) rational perception of our own individual existence as conscious persons; (b) the demon strable rationality of the existence of God or Supreme Mind; and (c) sense-perception of the existence of particular objects – as long as, but only as long as, they are actually present in sense. That each individual person exists is manifested to himself in memory, and no certainty beyond that of each passing thought while it passes can be greater than this. "If I doubt all other things," says Locke, after Descartes, "that very doubt makes me perceive my own existence, and will not suffer me to doubt of that" (iv. 9, 3). The eternal existence of God or Supreme Reason is with Locke only another way of expressing the principle of causality and suffi cient reason in its universality, as suggested by our conviction that our own personal existence had a beginning. Each individual per son knows that he now exists, and is convinced that he once had a beginning; with not less intuitive certainty of reason he knows that "nothing can no more produce any real being than it can be equal to two right angles." The final rational conclusion is that there must be eternally "a most powerful and most knowing Being, in which, as the origin of all, must be contained nil the perfec tions that can ever after exist," and out of which can come only what it has in itself, so that, as the adequate cause, it must involve mind. There is thus a rational necessity for Eternal Reason, or what we call God. He cautiously adds elsewhere, "Though I call the thinking faculty in me 'mind,' yet I cannot, because of that name, equal it in any thing to that infinite and incomprehensible Being which, for want of right and distinct conceptions, is called 'mind' also, or the eternal mind."
Turning from the metaphysics of religion to the metaphysics of matter, nearly – but perhaps not quite – all that one can affirm or deny about things external to us is, according to Locke, not knowledge but only presumptive trust. We have on the whole no knowledge of the real existence of anything other than our own individual existence, that of Universal Reason, and that of par ticular objects of sense – while, but only while, they are present to our senses. "When I see an external object at a distance, a man for instance, I cannot but be satisfied of his existence while I am looking at him. (Locke might have added that when one thus "sees a man" it is only his visible qualities that are perceived; for his other qualities are as little 'actual present sensations' as if he was out of the range of the senses altogether.) But when the man leaves me alone, I cannot be certain that he still exists. There is no necessary connexion between his existence a minute since (when he was present to my sense of sight) and his existence now (when he is absent from all my senses); by a thousand ways he may have ceased to be. I have not that certainty of his continued existence which we call knowledge; though the great likelihood of it puts it past doubt. But this is but probability and not knowledge" (chap. 11, § 9). Either a rationally intuitive or a rationally demonstrative science of Nature is thus, according to Locke, impossible. A conception of the co existences and successions of phenomena which form the external world being essentially the natural expression of the Universal Mind, and therefore capable of being reasoned about by our individual minds, in our gradual scientific progress towards agree ment between the objective thought in nature and our subjective thoughts, was too speculative and mystical for Locke. Pie prefers to urge the matter-of-fact consideration that all our interpretations
