separate class of individuals in the community who devoted themselves to the pacific profession of poetry.' The influence of the works of genius was illustrated also in the life of the ancient Athenians. 66 Among the Greeks," says an eloquent writer, "wherever the eyes were cast, the monuments of glory were to be found. The streets, the temples, the galleries, the porticos, all gave lessons to the citizens. Everywhere the people recognized the images of its great men; and beneath the purest sky, in the most beautiful fields, amid groves and sacred forests, and the most brilliant festivals of a splendid religion, surrounded with a crowd of orators and artists and poets, who all painted or modelled or celebrated or sang their compatriot heroes, marching, as it were, to the enchanting sounds of poetry and music that were animated with the same spirit, the Greeks, victorious and free, saw and felt and breathed nothing but the intoxication of glory and immortality." In modern times poetical and artistic productions do not exert so great an influence as they once did. Philosophy, science, history, and the practical pursuits of an advanced civilization engross the minds of men, and render them less susceptible to æsthetic influences. Nevertheless it is the part of wisdom to cherish the poet and the artist, and to encourage labors which, when rightly directed, tend to the elevation and refinement of

our race.

CHAPTER XLVI.

THE PHILOSOPHICAL IMAGINATION.

1. WE now turn to those uses of the imagination which are less exclusively connected with its own nature, and which do not belong distinctively to the reproductive phase of thought, but must be regarded either as occupying a middle ground or as forming parts of the discursive phase. With reference to these uses, three different modes of the imagination may be distinguished and characterized. They may be named the speculative, or scientific; the practical, or ethical; and the incentive, or motive.

Exercising the first of these, we form conceptions of fact or possibility, so as to assist our understanding of truth; using the second, we fashion plans and ideals for our practical realization; and employing the third, we stimulate our desires by placing before them definite aims and aspirations. The practical and the incentive imagination are fully considered in ethical writings, and in discussions relating to

the various forms of human motivity and effort. Our present study therefore may properly be limited to the philosophical imagination; this specially belongs to the domain of mental science.

Those who are accustomed to regard scientific discovery and invention as the peculiar and crowning work of man's reasoning faculties, may be surprised to hear that success in these labors depends greatly on the exercise of the imaginative power. We naturally surrender the ideal world to Homer and Virgil, Shakspeare and Milton, Dickens, DeFoe, and other kindred spirits; we regard Aristotle, Euclid, Kepler, Newton, Davy, Faraday, Agassiz, and the like, as men whose minds are wholly conversant about fact and reality.

But the truth is that philosophic investigation, which discovers the laws of Nature, and scientific invention, which discovers the modes in which these laws may be usefully applied, can make no progress without a vigorous employment of constructive and creative thought. This may not ordinarily be called imagination; it is certainly to be distinguished from that exercise of genius which the poet displays; yet it is of the same generic nature with this, and differs from it only because its operation is modified and controlled in the interest of a peculiar end,—namely, the rational pursuit of truth. We therefore discuss the scientific imagination in connection with the poetic, and regard both as developments of that one comprehensive faculty which has been called the productive imagination.

The scientific

with the

poetic imagination. Philosophical

At the same time we need not adopt an extreme infercompared ence from this doctrine, which some make. It has been taught that philosophic is so nearly allied to poetic talent that the same man may be expected to distinguish himself in both lines of effort, or at least to have the ability to do invention. So. The philosophic imagination endeavors to form correct conceptions of the working of causes as these operate in Nature, so that, by means of such conceptions, the operations of Nature may be anticipated and understood. In this mode of thought we are at liberty to imagine only what may naturally exist or happen under conditions which may naturally exist. We build upon fact, and employ the known elements and laws of actual existence so far as these may be applicable; and where they no longer apply, we still follow, as closely as possible. the analogy of Nature, and carefully shun whatever may conflict with real possibility. The poetic imagination, on the contrary, regards possibility only so far as not to offend by evident absurdity, and seeks conformity to Nature only in those features which may excite our sympathy and interest. Philosophic genius cares neither for the beautiful nor the affecting, but for the true and the probable; it may even co-exist with a very moderate sense of what is tasteful and pleasing; it avoids the weakening of scientific discourse by much æsthetic illustration. But the spirit of poetry delights in the graceful, the beautiful, the touching, the wonderful, the sublime, and aims at no other end than the production of such objects. It is plain that the disposition and habit of mind proper to the philosopher differ from, and even somewhat conflict with, those characteristic of the poet. A conjunction of the two forms of genius in one mind is not a thing to be expected, but rather the reverse; and, in point of fact, it would be

hard to find any instance in which the same person was eminent both as a poet and as a philosopher.

2. That form of imagination employed in speculative thought is sometimes known as philosophical invention, the term "invention" in this phrase being used in a wide sense, so as to include purely theoretical conjecture, as well as that which looks towards practice. This mode of imagination is always completed by supposing the object of it to be fact, that is, by distinctly uniting the idea of existence with that of the thing invented. Therefore the products of it, commonly, and with reference to their use, are called suppositions. For the rational faculty deals with, and conceives of, things only as subject to the laws of actual existence.

Different modes of philosophical invention may be distinguished according to the different ends for which suppositions are employed. These ends are three in number, — first, the discovery and ascertainment of truth; secondly, the application of truth, in deduction from things possible, and in useful invention; and, thirdly, the explanation and illustration of truth. These aims are not pursued in separation: they are so related that the attainment of one is often an important step in the prosecution of another; yet a special exercise of imagination, which belongs to each, may be distinctly conceived.

The imagination of discovery.

The philosopher is chiefly concerned with that mode of invention which seeks the discovery of truth. This is that which he himself employs; it is that, also, which calls most Hypothesis for elucidation and discussion. and supposiThe thought constructions tion distin- to which it gives rise are distinguished from other supposiguished and tions by the name "hypothesis." Originally, the terms "hydefined. pothesis" and "supposition," as their formation indicates, had the same meaning. They denoted those constructions of the imaginative power which we employ to explain phenomena, and in which causes and conditions are figuratively placed under those observed facts which are believed to rest or depend upon them.

This specific meaning is now retained by the word "hypothesis," which signifies a supposition used for the purpose of explaining phenomena, and, in connection with that, of showing its own truth or probability. For any hypothesis which rationally accounts for fact may be true; and if it be the only hypothesis by which the fact can be explained, it must be true. Supposition, on the other hand, has assumed the more general sense of imagining a thing to be fact, with reference to something which would follow if it were fact, whether that thing be the explanation of phenomena and the ascertainment of causes or not. When we speak of a supposition, we emphasize the conceived existence of the thing supposed; but in the idea of an hypothesis, the emphasis rests on the explanatory relation of the thing supposed to the facts immediately perceived. These remarks exhibit the reason on account of which a scientific conception, even though designed for purposes of explanation, is not commonly called an hypothesis, unless its explanatory value be immediately taken into account.

We should note, in passing, that the peculiar and specific meaning of the noun "hypothesis "is not always retained by the adjective "hypothetical." An hypothetical case is simply a supposed case; an

hypothetical syllogism means a syllogism in which one fact is supposed as the antecedent, not as the explanation, of another.

The twofold use of hypothesis.

While every hypothesis has a double end in view, — namely, to account for facts, and to ascertain whether the supposed cause exist or not,- some hypotheses aim more at the former, and others at the latter, of these ends. The famous speculation of Laplace respecting the origin and movement of planetary bodies is interesting chiefly as an explanation of phenomena. He conjectured that the atmosphere of the sun originally extended beyond the present limits of the solar system, and that planets were formed by the cooling and condensation of successive rings of fiery vapor, their orbital motion being caused by a combination of their centrifugal force with the centripetal attraction of the sun, and their diurnal motion by similar forces operating within each separate mass of matter. Scientific theories, in general, are principally valuable as explanatory of fact.

On the other hand, those hypotheses which are made in the course of judicial proceedings are mainly intended to show the truth or falsehood of the hypothesis itself. In a trial for murder, it was shown that a certain money-lender was discovered one morning in a wood beaten to death, and that this individual and the prisoner had entered that wood together the previous evening. It also appeared that the accused was a person of bad character, and had been a debtor to the murdered man in a considerable amount. The prosecution advocated the hypothesis that the prisoner had committed the crime in order to free himself from debt. The counsel for defence argued that the murder might have been committed by some other man. The jury found that the facts could be explained only on the hypothesis of the prisoner's guilt; and the man was executed. In this case the important question concerned, not the explanation of fact, but the correctness of the hypothesis.

Theory defined and character

ized.

Those systematic views of phenomena and their conditions, as mutually related, which hypotheses enable us to form, are called theories. A theory differs from an hypothesis in being more comprehensive, it includes, in one view, both fact and explanation. The conception of it, also, is less suggestive of unreality. One's theory of a phenomenon is a view confirmed by investigation and accepted with more or less confidence. His hypothesis respecting a phenomenon is a conjecture yet to be tested, and which may prove incorrect. While, therefore, these terms are allied, and may sometimes exchange places with each other, there is a difference. In particular, after an hypothesis may have been fully verified, we incline to speak no longer of it, but of the theory established by it

Before Newton's time, three laws of planetary motion had been discovered through the observations of Kepler. These were that the radius vector of a planet describes equal areas in equal times, that the path of every planet is an ellipse, and that the squares of the times of revolution of the different planets vary as the cubes of their mean distances from the sun. Newton conjectured that a force directed towards the centre of the sun, and varying inversely as the square of the distance from that point, would produce these phenomena; and

he was able to demonstrate that this was the only force which could produce them. Therefore, now, we speak not of the Newtonian hypothesis, but of the Newtonian theory, of solar attraction, or of universal gravitation.

Scientific

of it.

For

At the same time any digested view of fact, or of what idealization. may be assumed as fact, considered as united with its exThe reason planation, is properly termed a theory; and, indeed, the imaginative character of our hypotheses is often remarkably exhibited in those theories which originate from them. not only many theories have been constructed wholly by the imagination, with no aid from reason, and no reference to the analogy of Nature, but what is specially to be noted · - many even of those theories, in which the laws of existence are correctly set forth, present idealized objects and operations, such as are never to be met with in reality.

This separation of even correct hypothesis from literal fact, takes place whenever we desire to have an abstract or independent conception of the proper effect of some law. The powers of Nature do not work separately, nor do they always operate under the same conditions. Each plays its proportionate and variable part in producing the complex actualities which we see. In order to comprehend some simple law, we must conceive of a certain power acting alone under given conditions; and thus we form the conception of a phenomenon which never really takes place, yet which truly sets forth the operation of an existing law. We may conceive of an iron ball at rest in space, or driven forward into empty space, and thereafter free from the influence of every force save its own inertia or momentum. Then, with the aid of these conceptions, we state the law that any material body will forever maintain its condition of rest in the same place, or of motion in a right line and at the same rate of velocity, if it be not influenced by some external power. No such phenomena as these are ever witnessed; yet the phenomena actually observed justify our ideal conceptions and the law which they enable us to enunciate. The actual motion and rest of bodies obey this law, so far as the operation of other laws permit; and they can be accounted for by the combination of this law with others.

This power of forming and using ideal theories throws light on a class of objects sometimes considered in scientific thought, which differ, in point of perfection, from any that have ever been met with. The conditions of a law affecting any class of objects lie partly in the nature of the objects themselves; therefore the absolute, or perfect, exemplification of the law may call for a perfection in the nature of the object which is nowhere to be discovered. A perfect reflector which absorbs none at all of the light which falls upon it, or an absolutely opaque body through which no light can find its way, or a substance so transparent that light can pass through it without any even the slightest obstruction or diminution, has never been found. such objects can be imagined; and laws of optics, which apply approximately to real cases, can be formulated with reference to these imaginary standards. For realities sometimes approach so near perfection that no appreciable error follows from regarding them as perfect;

Yet