Truth is the object of Knowledge of whatever kind; and when we inquire what is meant by Truth, I suppose it is right to answer that Truth means facts and their relations, which stand towards each other pretty much as subjects and predicates in logic. All that exists, as contemplated by the human mind, forms one large system or complex fact, and this of course resolves itself into an indefinite number of particular facts, which, as being portions of a whole, have countless relations of every kind, one towards another. Knowledge is the apprehension of these facts, whether in themselves, or in their mutual positions and bearings. And, as all taken together form one integral subject for contemplation, so there are no natural or real limits between part and part; one is ever running into another; all, as viewed by the mind, are combined together, and possess a correlative character one with another, from the internal mysteries of the Divine Essence down to our own sensations and consciousness, from the most solemn appointments of the Lord of all down to what may be called the accident of the hour, from the most glorious seraph down to the vilest and most noxious of reptiles.
Now, it is not wonderful that, with all its capabilities, the human mind cannot take in this whole vast fact at a single glance, or gain possession of it at once. Like a short-sighted reader, its eye pores closely, and travels slowly, over the awful volume which lies open for its inspection. Or again, as we deal with some huge structure of many parts and sides, the mind goes round about it, noting down, first one thing, then another, as it best may, and viewing it under different aspects, by way of making progress towards mastering the whole. So by degrees [pg 046] and by circuitous advances does it rise aloft and subject to itself a knowledge of that universe into which it has been born.
These various partial views or abstractions, by means of which the mind looks out upon its object, are called sciences, and embrace respectively larger or smaller portions of the field of knowledge; sometimes extending far and wide, but superficially, sometimes with exactness over particular departments, sometimes occupied together on one and the same portion, sometimes holding one part in common, and then ranging on this side or that in absolute divergence one from the other. Thus Optics has for its subject the whole visible creation, so far forth as it is simply visible; Mental Philosophy has a narrower province, but a richer one. Astronomy, plane and physical, each has the same subject-matter, but views it or treats it differently; lastly, Geology and Comparative Anatomy have subject-matters partly the same, partly distinct. Now these views or sciences, as being abstractions, have far more to do with the relations of things than with things themselves. They tell us what things are, only or principally by telling us their relations, or assigning predicates to subjects; and therefore they never tell us all that can be said about a thing, even when they tell something, nor do they bring it before us, as the senses do. They arrange and classify facts; they reduce separate phenomena under a common law; they trace effects to a cause. Thus they serve to transfer our knowledge from the custody of memory to the surer and more abiding protection of philosophy, thereby providing both for its spread and its advance:—for, inasmuch as sciences are forms of knowledge, they enable the intellect to master and increase it; and, inasmuch as they are instruments, to communicate it readily to others. Still, after all, they [pg 047] proceed on the principle of a division of labour, even though that division is an abstraction, not a literal separation into parts; and, as the maker of a bridle or an epaulet has not, on that account, any idea of the science of tactics or strategy, so in a parallel way, it is not every science which equally, nor any one which fully, enlightens the mind in the knowledge of things, as they are, or brings home to it the external object on which it wishes to gaze. Thus they differ in importance; and according to their importance will be their influence, not only on the mass of knowledge to which they all converge and contribute, but on each other.
Since then sciences are the results of mental processes about one and the same subject-matter, viewed under its various aspects, and are true results, as far as they go, yet at the same time separate and partial, it follows that on the one hand they need external assistance, one by one, by reason of their incompleteness, and on the other that they are able to afford it to each other, by reason, first, of their independence in themselves, and then of their connexion in their subject-matter. Viewed altogether, they approximate to a representation or subjective reflection of the objective truth, as nearly as is possible to the human mind, which advances towards the accurate apprehension of that object, in proportion to the number of sciences which it has mastered; and which, when certain sciences are away, in such a case has but a defective apprehension, in proportion to the value of the sciences which are thus wanting, and the importance of the field on which they are employed.
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Let us take, for instance, man himself as our object of contemplation; then at once we shall find we can view [pg 048] him in a variety of relations; and according to those relations are the sciences of which he is the subject-matter, and according to our acquaintance with them is our possession of a true knowledge of him. We may view him in relation to the material elements of his body, or to his mental constitution, or to his household and family, or to the community in which he lives, or to the Being who made him; and in consequence we treat of him respectively as physiologists, or as moral philosophers, or as writers of economics, or of politics, or as theologians. When we think of him in all these relations together, or as the subject at once of all the sciences I have named, then we may be said to reach unto and rest in the idea of man as an object or external fact, similar to that which the eye takes of his outward form. On the other hand, according as we are only physiologists, or only politicians, or only moralists, so is our idea of man more or less unreal; we do not take in the whole of him, and the defect is greater or less, in proportion as the relation is, or is not, important, which is omitted, whether his relation to God, or to his king, or to his children, or to his own component parts. And if there be one relation, about which we know nothing at all except that it exists, then is our knowledge of him, confessedly and to our own consciousness, deficient and partial, and that, I repeat, in proportion to the importance of the relation.
That therefore is true of sciences in general which we are apt to think applies only to pure mathematics, though to pure mathematics it applies especially, viz., that they cannot be considered as simple representations or informants of things as they are. We are accustomed to say, and say truly, that the conclusions of pure mathematics are applied, corrected, and adapted, by mixed; but so too the conclusions of Anatomy, Chemistry, [pg 049] Dynamics, and other sciences, are revised and completed by each other. Those several conclusions do not represent whole and substantive things, but views, true, so far as they go; and in order to ascertain how far they do go, that is, how far they correspond to the object to which they belong, we must compare them with the views taken out of that object by other sciences. Did we proceed upon the abstract theory of forces, we should assign a much more ample range to a projectile than in fact the resistance of the air allows it to accomplish. Let, however, that resistance be made the subject of scientific analysis, and then we shall have a new science, assisting, and to a certain point completing, for the benefit of questions of fact, the science of projection. On the other hand, the science of projection itself, considered as belonging to the forces it contemplates, is not more perfect, as such, by this supplementary investigation. And in like manner, as regards the whole circle of sciences, one corrects another for purposes of fact, and one without the other cannot dogmatize, except hypothetically and upon its own abstract principles. For instance, the Newtonian philosophy requires the admission of certain metaphysical postulates, if it is to be more than a theory or an hypothesis; as, for instance, that what happened yesterday will happen to-morrow; that there is such a thing as matter, that our senses are trustworthy, that there is a logic of induction, and so on. Now to Newton metaphysicians grant all that he asks; but, if so be, they may not prove equally accommodating to another who asks something else, and then all his most logical conclusions in the science of physics would remain hopelessly on the stocks, though finished, and never could be launched into the sphere of fact.
Again, did I know nothing about the movement of [pg 050] bodies, except what the theory of gravitation supplies, were I simply absorbed in that theory so as to make it measure all motion on earth and in the sky, I should indeed come to many right conclusions, I should hit off many important facts, ascertain many existing relations, and correct many popular errors: I should scout and ridicule with great success the old notion, that light bodies flew up and heavy bodies fell down; but I should go on with equal confidence to deny the phenomenon of capillary attraction. Here I should be wrong, but only because I carried out my science irrespectively of other sciences. In like manner, did I simply give myself to the investigation of the external action of body upon body, I might scoff at the very idea of chemical affinities and combinations, and reject it as simply unintelligible. Were I a mere chemist, I should deny the influence of mind upon bodily health; and so on, as regards the devotees of any science, or family of sciences, to the exclusion of others; they necessarily become bigots and quacks, scorning all principles and reported facts which do not belong to their own pursuit, and thinking to effect everything without aid from any other quarter. Thus, before now, chemistry has been substituted for medicine; and again, political economy, or intellectual enlightenment, or the reading of the Scriptures, has been cried up as a panacea against vice, malevolence, and misery.