All knowledge is essentially one. The object-matter upon which intellect exerts itself, does not affect the subjective act of knowing. Physics, when stripped of that which is merely contingent, becomes metaphysics. Physical science deals with object-matter, and discusses the signs by which nature communicates her message—that is, phenomena. Metaphysical science has to do with the subject-mind, and discusses the meaning of the message. The one converts God's hieroglyphics into easily-intelligible language; the other translates this language into Idea. If this be true, there must be a unity of method in all science, however great the diversity of the object-matter investigated. This method is subjectively determined, that is, by the constitution of the mind, and not by the particular form of matter upon which intellectual energy may be exerted. If there is an essential unity in all knowledge, it is because there is a corresponding unity of method in all mental activity. It is only when we look upon what is to be known, that truth separates into sciences; but particular truths become particular sciences only under assumed relations to the whole of which they form a part.

Objectively considered, science is classified knowledge; subjectively viewed, it is the laws or principles according to which knowledge is classified. Every actor implies an act—every thinker a thought. We may therefore universally make this dual classification, according as we view the mental operation involved, or the attributes of objects which form the subject of thought. The possibility of science is conditioned upon the possibility of classification. Mere knowledge is not science, as the world ought to have learned by costly experience. Even classified knowledge may not be science; it becomes science not through previous classification, but in the act of being classified, and therefore only as the principle of classification is apprehended—that is, only as the particular application of the law of generalization is distinctly recognized. A man may know a book and know nothing more; he knows the science only when he is capable of making the book for himself. Mere knowledge thus differs from science in that the one is held only by the apprehensive powers of the mind, while the other passes beyond these into the reflective or ratiocinative. Pure science, then, must be wholly abstract. The forms and substances of Nature with which the scientific student deals, are only the discrete figures of the young mathematician, to be thrown aside with advancing knowledge. Matter is only the staff on which the mind leans, while too feeble to go alone. It is not the finely chiseled statue that renders a man a sculptor; it is the conception which is therein embodied. A day-laborer may have cut the stone, but only the artist could conceive the idea. So in science, we care but little for the particular results at which we arrive, compared with the laws, according to which the results have been attained.

But conceptions cannot be communicated without being rendered objective. The ideal of the artist is locked up in his own mind, until on canvas, in marble, or by means of some other physical symbol, he communicates his high imaginings. Matter, then, according to the present constitution of things is the condition of intellectual communication. Law cannot be studied as abstract law; it can be studied only while acting, and that which exhibits this activity must be matter—something which will always and uniformly obey. There can be no conception of force except as acting, and the sole medium of such activity is matter. Thus again, matter is the condition of all communication from nature to man. Science is thus, in a measure, determined by the conditions of its discovery and communication. But we must distinguish between an invariable condition and that which is thus conditioned. Matter is not science; it is only the condition of its discovery and communication. Air is not hearing; it is the condition of hearing. We do not study matter for the sake of the matter when we study science, but for the sake of the law communicated to us in these changes of matter, and Law is a metaphysical, not a physical idea. Reason, not sense, apprehends it. Law is, so to speak, formulated in the physical, but it is not material. Matter is only the vehicle of science, as language is the vehicle of thought.

It is plain, then, that just as in mathematics we have a division into pure and mixed, according as we deal with matter in the abstract or in the concrete, so we may in any science make a corresponding division, according as we confine our attention to the laws revealed by matter or to the matter revealing the laws: in other words; just as we give attention to the ideas of the message, or to the language in which it is communicated. The language must first be learned, but the words used to communicate the message may be separately understood, and yet the meaning of the message wholly missed. Knowing only the one makes a charlatan; knowing the other makes a savan. The sciences based upon this objective study of Nature are denominated Natural Sciences; and because they lisp the first syllables of Nature's message to man, they should be his primary teachers. It is by their aid that the universal message of God to man must be read. They form, as it were, a public highway leading from Nature to God. But the difficulty is that observing men become so absorbed in admiring some splendid piece of Divine engineering that they stop to gaze and wonder, until losing sight of everything above and beyond, they refuse to advance, fondly imagining that they have reached the end of the journey.

The science based upon this subjective study of Nature is called metaphysics. Logic has been defined as "The Science of Thought;" it should be termed "The Science of Thinking." It is not a dead body which we are studying by dissection, but a living, vital Force, which we study by observing its activities. We find here the same error which we find elsewhere—a stopping with the material symbol, and an ignoring of the intellectual force which clothed itself with the symbol. Astronomy is not the science of circles and spheres, ellipses and ellipsoids, but of the Force whose sensible utterances are given in these curves. We might as well call Painting the science of pictures, or Sculpture the science of statues. So Language, the medium of thought, is only a symbol, less material indeed than pictures and statues, but still physical. What we want in "The Science of Thinking" is not the knowledge of symbols, but the knowledge of that which is symbolized. The chemist does not care for the compounds he finds in his retort; he seeks after the truth which these compounds formulate. Metaphysics and Physics evidently agree in this; that both are seeking to frame an articulate utterance of the Idea given in the diverse manifestations of Force—the Idea which includes all Potencies, the summing up of all phenomena into that final generalization which includes the intellectual as well as the material, until at last we reach the essential unity of all Truth.

Science, then, is classification, or the discovery of the principles of classification, rather than an arbitrary acquaintance with things classified. Every science, however, must have an objective expression—that is, must be formulated. In this, both metaphysical and physical science agree; the only difference in this respect is, that in Physics, Nature gives us in the first place the material interpretation of the idea—that is, the basis of classification—which we have only to translate into idea: while in metaphysics, we first have the idea to which we must furnish the objective utterance. We see here the precise difference between what is called the logical and the natural method—the one being usually called the reverse of the other. The difference is not so much a difference in intellectual procedure as in objective expression. For instance: The botanist has before him the whole range of vegetable forms. He notes resemblances and differences, and groups plants into species and genera, but his work is not ended when these are named and known, and their qualities discovered. He is seeking amidst these multifarious forms for the law of vegetable growth and reproduction. Every organ of the plant is the symbol of an idea, and these ideas form the science of Botany. These Ideas are metaphysical—that is intellectual, and only their sensible manifestation is physical. The symbols of these Ideas, being given in Nature, must be learned from observation before they can be used intelligently, just as words must be learned before one can speak a language. Mastery of the means of expression is as essential to the communication of ideas an is the possession of the ideas themselves. The botanist observes an individual plant, and notes its characteristics. He observes others which possess some of these characteristics whilst others are wanting. He forms a class-type from these agreeing attributes, and gives this new collocation of characteristics a name. Nature never presents this class-type absolutely; it is found nowhere but in intellect. What has the botanist done but to retranslate the communication of Nature into Idea, and then to express this idea by less complicated and less physical symbols? Man's province in this case is simply to interpret the hieroglyphics of Nature into a more readily comprehended language—to express that simply which nature has expressed confusedly. The scientist restricts himself to the interpretation of a single class of symbols, as the Botanist to plants, the Zoologist to animals, but the end sought in each case is the same—that is, to change all these physical utterances of Nature into Idea, and to secure for this Idea a method of expression involving the least possible materiality of symbol—that is, to change individual facts and phenomena into general principles, which, because abstract, are unchangeable. When this has been done, the work of the Naturalist ceases, but the work of Man, the Thinker is not done; it is only just begun. By assuming the ultimate expressions of the various natural sciences as individual and not as typical, we can treat the truths reached by them precisely as the Botanist treated plants, and, rejecting points of of difference, may find in them all some central idea. This is the province of the metaphysician. He seeks the law of Idea, he determines the law of Thinking, just as all other laws are determined, from a study of the symbols formulating its expression in Nature. When this law has been distinctly enunciated, and freed from all intermixture with the contingent, then the work of the metaphysician ceases, the summum genus has been reached. The truths communicated in the symbols of Nature, have been correlated and enunciated, and finally translated from the dialect of man the physical into the language of man the intellectual. Physical science determines the separate words of this message of God, the letters of which are scattered throughout Nature. Metaphysics combines these words into propositions which enunciate a distinct truth. There is therefore neither conflict nor variation between the method of Logic and the method of Nature. The movement of both is in the same direction; the only difference is in the point of starting. And another truth no less important, which follows from the foregoing discussion, is that the method of Nature is fundamental to the method of Logic. Physics should precede metaphysics, but not exclude it; both are essential to every true science, and physics, which stops with physics, leads man by dazzling promises into some Utopian desert only to leave him there to die of hunger. And it is no less true that metaphysics, without this basis in experimental science, is illusory and untrustworthy, wherever the original data are necessarily empirical.

Two conditions are thus necessary to all science: a body of knowable truth capable of being systematized; and an intelligence capable of apprehending and systematizing it. One of these conditions is physical and one is metaphysical; and all true science must be the resultant of Law and Idea, the Objective and the Subjective, the twin forces of Nature and Man. If either of these conditions be wanting, there can be no true science, for science can neither be "evolved from the depths of the personal consciousness," nor can the scattered letters of scientific truth, as given in nature, arrange themselves into the words of a significant message. Knowledge must be classified before it is science, and that which classifies can only be intellect—discovering and enunciating this classification according to the laws of mental action. As prominence is given to one or other of these two conditions we have the division into Logical and Natural, but the fundamental principle of classification is the same in both—it being simply the law of intellectual action—just as the law which governs the action of the levers of a loom will determine the pattern of the woven fabric. There can, therefore, be no conflict between the methods of Logic and those of Nature. The determining element in all classification, whether of the phenomena of Mind or of the grosser phenomena of Matter is uniformly and always the same—the law of intellectual action.

Science then resolves itself into a determination of this Law of mental activity, so that in an ultimate analysis, all science is metaphysical, just as all science primarily is physical. Here, as elsewhere, Law can be studied only in its objective manifestations. The Law of Thinking can be educed only from expressed Thought, but the Law is not objective thought, any more than the idea of the sculptor is marble, or the conception of the painter is paint. The simplest expression of thought is not the syllogism but the logical proposition. Now, it is plain that if the proposition is the formulation—the material representative of thought—if we study it as we study other natural symbols, we will find in it the fundamental Law of Thinking, and ultimately the fundamental Law of all Science: just as, if it were possible to reduce all elementary substances to one, the chemist would be able to find in that one a condensed expression of chemical science.

What then is a proposition? Simply stated, it is the assertion of relation between two terms; or more abstractly, it is the reference of an individual to its species—the assertion of a classification. We find here the same duality which we noticed above. If we give prominence to the individual notion, we consider the proposition in extension; if we turn our attention to the specific notion we consider the proposition in intention: in the one case referring to the individuals composing the class, in the other to the attributes composing the class-type. The first corresponds to induction, the second to deduction. When we study individuals we study physics; when we study the attributes composing the class-type, we study metaphysics. The Law of Thinking as educed from a study of the proposition is the law of classification. The proposition, considered affirmatively, asserts explicitly agreement between certain attributes of two terms; that is, it asserts a classification. The aim of science is to reach this proposition, to discover and assert the principle of classification—in other words, to formulate metaphysically what nature has presented physically. We must find, then, the first or fundamental law of thinking in this integration or classification. This fundamental law may be subdivided into two species, according to the two terms of the proposition; of which the first may be stated thus: "Every possible object of thought is to a certain extent identical with every other"; and as the proposition implicitly states disagreement, the second may be stated thus: "Every possible object of thought is to a certain extent diverse from every other." The first gives the positive (subjective) condition of the proposition, the second the negative (objective) condition: both together constitute the conditions of thinking. The proposition is thus the assertion of the same in the different. The proposition also asserts, implicitly, the tertium quid, or the basis of classification—the class-type, to which both terms are referred—that is, the proposition secondarily asserts an analysis. According to the first condition we have the inductive process; according to the second we have the deductive process. A complete movement of idea from its purely physical symbolization to its metaphysical interpretation, must involve both these processes.

The mind possesses the power of analysis; it can watch its own operations and retrace its steps, until it arrives at the original data of consciousness; but analysis cannot comprise the whole of the logical process. Before there can be analysis there must be something to be analyzed; before steps can be retraced, they must be taken. We must not confound a condition with a Law—the one is a conception antecedent to all action, a genus to which the particular activity may be referred; the other is coincident with action. The one is the medium of the other. We may illustrate this idea by science itself, which is reached only by an analysis of Art. Matter is the condition of the expression of an idea; hence to all but the artist, Art must precede Science, but this cannot be in the case of the artist; in his mind the Idea is first conceived, and there it is given expression in the forms of Art. Here, as uniformly in Nature, the whole absolutely precedes the part—the universal exists before the particular—God before man. Truth absolute thus exists before truth conditioned. Science before Art. Remove conditions and the conditioned becomes the absolute; art and science coincide. But truth which is assumed to be out of all relations, cannot be comprehended by man, and practically is not. Even the universal propositions of deduction express universality under conditions—that is universality of relation; just as infinity in mathematics means that which passes measurement, while in fact between infinity and measurement there is no relation, and the infinite is thus incomprehensible as an object of thought, although by no means unrecognizable as a necessary condition antecedent to all intellectual action. It is of vital importance that we note this distinction, because reasoning, i. e. classification, is possible only so long as we deal with what is admitted to be under relation: if we assume a term to be out of all relation, it ceases to be an object of thought—it can neither be classified nor unclassified; it is beyond reason. Mathematics can proceed with its investigations only so long as it treats all quantities as measurable; it must wholly cease its calculations if an infinite term be introduced. To claim that analysis represents the complete normal action of the intellect in reasoning, is ultimately to claim that the initial point of thinking is the summum genus of thought—God. Now God is undoubtedly the initial point of absolute thought, but he is not the beginning of human thought. Intellectually speaking, God is the final generalization; every movement possible to him must be one of analysis—a differentiation of Himself, so to speak, by negatives. Thus the course of absolute Thought, beginning with God, must be first towards a complete differentiation into ultimate individualization; and lastly a complete integration again of individuals into an infinite whole. This dual action completes the circle of intellectual activity. We have dropped attribute after attribute until we have reached the last possible analysis; but we do not stop here, but by the assumption of attributes we again reach the highest possible synthesis. This must be the method of the divine activity, successive differentiation and integration, the closing in of a mighty circle of infinity, embracing all the finite, but never losing the essential characteristic of the infinite.

Now, if this also represent the exact movement of the finite mind in action—that is, in reasoning, man must be God. Man is finite. Even his infinite is only the immeasurable—not that which is without the category of measure. He cannot begin where the Infinite begins, at the highest possible generalization,—but he must begin with the finite. If what we have shown above be true, man must begin with the individual, and the first mental act of the positive character of thinking, is the reference of this individual notion to a class. Now the class-notion is the same as the individual notion, less certain attributes as individual attributes, but gathered into a larger whole. This process is plainly integration; we are rejecting from the new conception whatever prevents enlarging the class. Each higher generalization involves all the attributes of the lower, not individually, but specifically or generically. In the final generalization, extension and intension coalesce. Just as we reach the individual by differentiating a universal through successive negations, we reach the universal again, by integration, by successively denying the negations through which we just now differentiated. The movement of the finite mind in reasoning is thus from the individual through the universal to the individual again.

Science thus parts into two great branches—one seeking to establish principles by what we have called integration, and the other the elucidation of facts by a priori reasoning instead of observation. That is, the aim of true science is to free man from the restrictions of the finite, and to place him in possession of the infinite—the closing in of a lesser circle of infinite truth, yet never losing hold upon the finite. In accordance with this view we see science pursuing its integrations until it has identified as composing an essential unity all the various manifestations of force. This is the finite becoming the infinite, for unity is, in so far, infinity—God is one, a unity, not a unit. But we also see science going beyond this point, and by a new series of differentiations reaching truths new to experience, if indeed not impossible to experience.

Between these two limits all knowledge is forever moving. It can never rest. The tide of thought sweeps onward towards the infinite—God following it to its final absorption into the I Am, simple being,—while finite man, because of his finiteness, can only reach those universals which are infinite only to human thought. Like men on a journey we leave the train when we have reached our journey's end, but the train passes on out of sight in the distance, sending back, now and then, tokens of its progress, as it thunders over a bridge, or whistles shrill as it nears some further stopping place, until at last all is still, not because the train has stopped, but because we can follow it no further with our senses. Even after science has reached the utmost limit possible to it, it is not satisfied to rest there, but starts at once upon its return trip, to bring to notice undiscovered facts hidden in these mighty generalizations. Thus the pendulum of intellectual activity unceasingly vibrates between the infinite and the finite, never resting, because Idea and Matter, the force of Man and the force of Nature can never be completely identified.