who can say*, even in the heat of debate, or the recklessness of anonymous criticism, that "in all these fundamental discoveries appropriate ideas had no share," and that the discoveries "might have been made by the most ordinary observers." 21. I have now, I trust, shown in various ways, how the Explication of Conceptions, including in this term their clear development from Fundamental Ideas in the discoverer's mind, as well as their precise expression in the form of Definitions or Axioms, when that can be done, is an essential part in the establishment of all exact and general physical truths. In doing this, I havee ndeavoured to explain in what sense the possession of clear and appropriate ideas is a main requisite for every step in scientific discovery. That it is far from being the only step, I shall soon have to show; and if any obscurity remain on the subject treated of in the present chapter, it will, I hope, be removed when we have examined the other elements which enter into the constitution of our knowledge. CHAPTER III. OF FACTS AS THE MATERIALS OF SCIENCE. WE have now to examine how science is built up by the combination of facts. In doing this, we suppose that we have already obtained a supply of definite and certain facts, free from obscurity and doubt. We must, therefore, first consider under what conditions facts can assume this character. * This is said by the Edinburgh Reviewer of my History, in an attempt to disprove the necessity of clear and appropriate ideas for discovery. Ed. Rev., No. cxxxiii., p. 122. When we inquire what facts are to be made the materials of science, perhaps the answer which we should most commonly receive would be, that they must be true facts, as distinguished from any mere inferences or opinions of our own. We should probably be told that we must be careful in such a case to consider as facts only what we really observe: that we must assert only what we see; and believe nothing except upon the testimony of our senses. But such maxims are far from being easy to apply, as a little examination will convince us. 1. It has been explained in the preceding part of this work that all perception of external objects and occurrences involves an active as well as a passive process of the mind;—includes not only sensations, but also ideas by which sensations are bound together, and have a unity given to them. From this it follows that there is a difficulty in separating in our perceptions what we receive from without, and what we ourselves contribute from within;—what we perceive, and what we infer. In many cases, this difficulty is obvious to all: as, for example, when we witness the performances of a juggler or a ventriloquist. In these instances we imagine ourselves to see and to hear what certainly we do not see and hear. The performer takes advantage of the habits by which our minds supply interruptions and infer connexions; and by giving us fallacious indications, he leads us to perceive as an actual fact, what does not happen at all. In these cases it is evident that we ourselves assist in making the fact; for we make one which does not really exist. In other cases, though the fact which we perceive be true, we can easily see that a large portion of the perception is our own act; as when from the sight of a bird of prey we infer a carcass, or when we VOL. II. read a half-obliterated inscription. In the latter case, the mind supplies the meaning, and perhaps half the letters; yet we do not hesitate to say that we actually read the inscription. Thus, in many cases, our own But inferences and interpretations enter into our facts. this happens in many instances in which it is at first sight less obvious. When any one has seen an oak-tree blown down by a strong gust of wind, he does not think of the occurrence any otherwise than as a fact of which he is assured by his senses. Yet by what sense does he perceive the force which he thus supposes the wind to exert? By what sense does he distinguish an oak-tree from all other trees? It is clear upon reflection, that in such a case, his own mind supplies the conception of extraneous impulse and pressure, by which he thus interprets the motions observed, and the distinction of different kinds of trees according to which he thus names the one under his notice. The idea of force, and the idea of definite resemblances and differences, are thus combined with the impressions on our senses, and form an undistinguished portion of that which we consider as the fact. And it is evident that we can in no other way perceive force, than by seeing motion; and cannot give a name to any object without not only seeing a difference of single objects, but supposing a difference of classes of objects. When we speak as if we saw impulse and attraction, things and classes, we really see only objects of various forms and colours, more or less numerous, variously combined. But do we really perceive so much as this? When we see the form, the size, the number, the motion of objects, are these really mere impressions on our senses, unmodified by any contribution or operation of the mind itself? A very little attention will suffice to convince us that this is not the case. When we see a windmill turning, it may happen, as we have elsewhere noticed*, that we mistake the direction in which the sails turn: when we look at certain diagrams, they may appear either convex or concave: when we see the moon first in the horizon and afterwards high up in the sky, we judge her to be much larger in the former than in the latter position, although to the eye she subtends the same angle. And in these cases and the like, it has been seen that the error and confusion which we thus incur arise from the mixture of acts of the mind itself with impressions on the senses. But such acts are, as we have also seen, inseparable portions of the process of perception. A certain activity of the mind is involved, not only in seeing objects erroneously, but in seeing them at all. With regard to solid objects, this is generally acknowledged. When we seem to see an edifice occupying space in all dimensions, we really see only a representation of it as it appears referred by perspective to a surface. The inference of the solid form is an operation of our own, alike when we look at a reality and when we look at a picture. But we may go further. Is plane figure really a mere sensation? If we look at a decagon, do we see at once that it has ten sides, or is it not necessary for us to count them: and is not counting an act of the mind? All objects are seen in space; all objects are seen as one or many: but are not the idea of space and the idea of number requisite in order that we may thus apprehend what we see? That these ideas of space and number involve a connexion derived from the mind and not from the senses, appears, as we have already seen, from this, that those ideas afford us the materials of universally and necessary truths: such truths as the senses cannot possibly supply. And thus even the perception of such facts as the size, shape, and number of objects, cannot be said to be impressions of sense, distinct from Vol. i. p. 112. all acts of mind, and cannot be expected to be free from error on the ground of their being mere observed facts. Thus the difficulty which we have been illustrating, of distinguishing facts from inferences and from interpretations of facts, is not only great, but amounts to an impossibility. The separation at which we aimed in the outset of this discussion, and which was supposed to be necessary in order to obtain a firm groundwork for science, is found to be unattainable. We cannot obtain a sure basis of facts by rejecting all inferences and judgments of our own, for such inferences and judgments form an unavoidable element in all facts. We cannot exclude our ideas from our perceptions, for our perceptions involve our ideas. 2. But still it cannot be doubted that in selecting the facts which are to form the foundation of science, we must reduce them to their most simple and certain form; and must reject everything from which doubt or error may arise. Now since this, it appears, cannot be done, by rejecting the ideas which all facts involve, in what manner are we to conform to the obvious maxim that the facts which form the basis of science must be perfectly definite and certain? The analysis of facts into Ideas and Sensations, which we have so often referred to, suggests the answer to this inquiry. We are not able, nor need we endeavour, to exclude ideas from our facts, but we may be able to discern, with perfect distinctness, the ideas which we include. We cannot observe any phenomena without applying to them such ideas as space and number, cause and resemblance, and usually several others; but we may avoid applying these ideas in a wavering or obscure manner, and confounding ideas with one another. We cannot read any of the inscriptions which nature presents to us, without interpreting them by means of some language which |
