If these premisses are admitted, we are led to a conclusion which is of great value for the purpose of this Introduction. For, if the measure of civilization is the triumph of the mind over external agents, it becomes clear, that of the two classes of laws which regulate the progress of mankind, the mental class is more important than the physical. This, indeed, is assumed by one school of thinkers as a matter of course, though I am not aware that its demonstration has been hitherto attempted by any thing even approaching an exhaustive analysis. The question, however, as to the originality of my arguments, is one of very trifling moment; but what we have to notice is, that in the present stage of our inquiry, the problem with which we started has become simplified, and a discovery of the laws of European history is resolved, in the first instance, into a discovery of the laws of the human mind. These mental laws, when ascertained, will be the ultimate basis of the history of Europe; the physical laws will be treated as of minor importance, and as merely giving rise to disturbances, the force and the frequency of which have, during several centuries, perceptibly diminished.
If we now inquire into the means of discovering the laws of the human mind, the metaphysicians are ready with an answer; and they refer us to their own labours as supplying a satisfactory solution. It therefore becomes necessary to ascertain the value of their researches, to measure the extent of their resources, and, above all, to test the validity of that method which they always follow, and by which alone, as they assert, great truths can be elicited.
The metaphysical method, though necessarily branching into two divisions, is, in its origin, always the same, and consists in each observer studying the operations of his own mind.292 This is the direct opposite of the historical method; the metaphysician studying one mind, the historian studying many minds. Now, the first remark to make on this is, that the metaphysical method is one by which no discovery has ever yet been made in any branch of knowledge. Every thing we at present know has been ascertained by studying phenomena, from which all casual disturbances having been removed, the law remains as a conspicuous residue.293 And this can only be done by observations so numerous as to eliminate the disturbances, or else by experiments so delicate as to isolate the phenomena. One of these conditions is essential to all inductive science; but neither of them does the metaphysician obey. To isolate the phenomenon is for him an impossibility; since no man, into whatever state of reverie he may be thrown, can entirely cut himself off from the influence of external events, which must produce an effect on his mind, even when he is unconscious of their presence. As to the other condition, it is by the metaphysician set at open defiance; for his whole system is based on the supposition that, by studying a single mind, he can get the laws of all minds; so that while he, on the one hand, is unable to isolate his observations from disturbances, he, on the other hand, refuses to adopt the only remaining precaution – he refuses so to enlarge his survey as to eliminate the disturbances by which his observations are troubled.294
This is the first and fundamental objection to which metaphysicians are exposed, even on the threshold of their science. But if we penetrate a little deeper, we shall meet with another circumstance, which, though less obvious, is equally decisive. After the metaphysician has taken for granted that, by studying one mind, he can discover the laws of all minds, he finds himself involved in a singular difficulty as soon as he begins to apply even this imperfect method. The difficulty to which I allude is one which, not being met with in any other pursuit, seems to have escaped the attention of those who are unacquainted with metaphysical controversies. To understand, therefore, its nature, it is requisite to give a short account of those two great schools, to one of which all metaphysicians must necessarily belong.
In investigating the nature of the human mind, according to the metaphysical scheme, there are two methods of proceeding, both of which are equally obvious, and yet both of which lead to entirely different results. According to the first method, the inquirer begins by examining his sensations. According to the other method, he begins by examining his ideas. These two methods always have led, and always must lead, to conclusions diametrically opposed to each other. Nor are the reasons of this difficult to understand. In metaphysics, the mind is the instrument as well as the material on which the instrument is employed. The means by which the science must be worked out, being thus the same as the object upon which it works, there arises a difficulty of a very peculiar kind. This difficulty is, the impossibility of taking a comprehensive view of the whole of the mental phenomena; because, however extensive such a view may be, it must exclude the state of the mind by which, or in which, the view itself is taken. Hence we may perceive what, I think, is a fundamental difference between physical and metaphysical inquiries. In physics, there are several methods of proceeding, all of which lead to the same results. But in metaphysics, it will invariably be found, that if two men of equal ability, and equal honesty, employ different methods in the study of the mind, the conclusions which they obtain will also be different. To those who are unversed in these matters, a few illustrations will set this in a clearer light. Metaphysicians who begin by the study of ideas observe in their own minds an idea of space. Whence, they ask, can this arise? It cannot, they say, owe its origin to the senses, because the senses only supply what is finite and contingent; whereas the idea of space is infinite and necessary.295 It is infinite, since we cannot conceive that space has an end; and it is necessary, since we cannot conceive the possibility of its non-existence. Thus far the idealist. But the sensualist, as he is called,296– he who begins, not with ideas, but with sensations, arrives at a very different conclusion. He remarks that we can have no idea of space until we have first had an idea of objects; and that the ideas of objects can only be the results of the sensations which those objects excite. As to the idea of space being necessary, this, he says, only results from the circumstance that we never can perceive an object which does not bear a certain position to some other object. This forms an indissoluble association between the idea of position and the idea of an object; and as this association is constantly repeated before us, we at length find ourselves unable to conceive an object without position, or, in other words, without space.297 As to space being infinite, this, he says, is a notion we get by conceiving a continual addition to lines, or to surfaces, or to bulk, which are the three modifications of extension.298 On innumerable other points we find the same discrepancy between the two schools. The idealist,299 for example, asserts that our notions of cause, of time, of personal identity, and of substance, are universal and necessary; that they are simple; and that not being susceptible of analysis, they must be referred to the original constitution of the mind.300 On the other hand, the sensationalist, so far from recognizing the simplicity of these ideas, considers them to be extremely complex, and looks upon their universality and necessity as merely the result of a frequent and intimate association.301
This is the first important difference which is inevitably consequent on the adoption of different methods. The idealist is compelled to assert, that necessary truths and contingent truths have a different origin.302 The sensationalist is bound to affirm that they have the same