g. That the progress of Physiology may throw a new light on Psychology is a dream in which scientific men are always tempted to indulge. But however certain we may be of the connexion between mind and body, the explanation of the one by the other is a hidden place of nature which has hitherto been investigated with little or no success.
h. The impossibility of distinguishing between mind and body. Neither in thought nor in experience can we separate them. They seem to act together; yet we feel that we are sometimes under the dominion of the one, sometimes of the other, and sometimes, both in the common use of language and in fact, they transform themselves, the one into the good principle, the other into the evil principle; and then again the 'I' comes in and mediates between them. It is also difficult to distinguish outward facts from the ideas of them in the mind, or to separate the external stimulus to a sensation from the activity of the organ, or this from the invisible agencies by which it reaches the mind, or any process of sense from its mental antecedent, or any mental energy from its nervous expression.
i. The fact that mental divisions tend to run into one another, and that in speaking of the mind we cannot always distinguish differences of kind from differences of degree; nor have we any measure of the strength and intensity of our ideas or feelings.
j. Although heredity has been always known to the ancients as well as ourselves to exercise a considerable influence on human character, yet we are unable to calculate what proportion this birth-influence bears to nurture and education. But this is the real question. We cannot pursue the mind into embryology: we can only trace how, after birth, it begins to grow. But how much is due to the soil, how much to the original latent seed, it is impossible to distinguish. And because we are certain that heredity exercises a considerable, but undefined influence, we must not increase the wonder by exaggerating it.
k. The love of system is always tending to prevail over the historical investigation of the mind, which is our chief means of knowing it. It equally tends to hinder the other great source of our knowledge of the mind, the observation of its workings and processes which we can make for ourselves.
l. The mind, when studied through the individual, is apt to be isolated—this is due to the very form of the enquiry; whereas, in truth, it is indistinguishable from circumstances, the very language which it uses being the result of the instincts of long-forgotten generations, and every word which a man utters being the answer to some other word spoken or suggested by somebody else.
III. The tendency of the preceding remarks has been to show that Psychology is necessarily a fragment, and is not and cannot be a connected system. We cannot define or limit the mind, but we can describe it. We can collect information about it; we can enumerate the principal subjects which are included in the study of it. Thus we are able to rehabilitate Psychology to some extent, not as a branch of science, but as a collection of facts bearing on human life, as a part of the history of philosophy, as an aspect of Metaphysic. It is a fragment of a science only, which in all probability can never make any great progress or attain to much clearness or exactness. It is however a kind of knowledge which has a great interest for us and is always present to us, and of which we carry about the materials in our own bosoms. We can observe our minds and we can experiment upon them, and the knowledge thus acquired is not easily forgotten, and is a help to us in study as well as in conduct.
The principal subjects of Psychology may be summed up as follows:—
a. The relation of man to the world around him,—in what sense and within what limits can he withdraw from its laws or assert himself against them (Freedom and Necessity), and what is that which we suppose to be thus independent and which we call ourselves? How does the inward differ from the outward and what is the relation between them, and where do we draw the line by which we separate mind from matter, the soul from the body? Is the mind active or passive, or partly both? Are its movements identical with those of the body, or only preconcerted and coincident with them, or is one simply an aspect of the other?
b. What are we to think of time and space? Time seems to have a nearer connexion with the mind, space with the body; yet time, as well as space, is necessary to our idea of either. We see also that they have an analogy with one another, and that in Mathematics they often interpenetrate. Space or place has been said by Kant to be the form of the outward, time of the inward sense. He regards them as parts or forms of the mind. But this is an unfortunate and inexpressive way of describing their relation to us. For of all the phenomena present to the human mind they seem to have most the character of objective existence. There is no use in asking what is beyond or behind them; we cannot get rid of them. And to throw the laws of external nature which to us are the type of the immutable into the subjective side of the antithesis seems to be equally inappropriate.