Whatever be the pretensions it makes, physiology has hitherto thrown little light on purely mental phenomena, and none whatever on higher mental action, such as ratiocination, the idea of the good, and resistance to temptation.
Secondly, the metaphysician must enter the physiological field.He must, if he can, conduct researches;he must at least master the ascertained facts.He must not give up the study of the nervous system and brain to those who cannot comprehend any thing beyond what can be made patent to the senses or disclosed to the microscope.I do cherish the hope that physiological psychology may in the end be rewarded by valuable discoveries.Light may be thrown on purely mental action by the fact that sensory action travels to the brain at the rate of 144.32 feet in the second, and from the brain at the rate of 108.24; that the movement is slowest in the case of the sense of sight and quickest in touch; and by what is alleged by Donders that a thought requires 1/26 of a second.There are mental actions which cannot well be explained by mental laws, such as the rise of certain states and the association of certain states; the rise, for instance, and the association of cheerful thoughts in the time of health, and of gloomy thoughts when we are laboring under derangement of the stomach.There may here be latent processes which do not fall under consciousness, but may be detected by the microscope or chemical analysis.By such researches the results reached by the psychologist may be so far modified on the one hand and considerably widened on the other.But all such investigations should be conducted by those who can understand and appreciate the peculiar nature of mental phenomena, and allow them their full and legitimate space.
No physiologist can talk of, {459} or so much as refer to, mental action without speaking of feelings, affections, thoughts, fancies, imaginations, desires, purposes, resolves; but no eye, no mechanical instrument, can detect these.They cannot be weighed in the balance or measured by the line.There is a division of the mental faculties commonly adopted in the present day into the senses and the intellect, the emotions and the will; but this distribution is suggested by the inward sense, and could never be discovered by an inspection of the compartments of the brain.
III.Metaphysics will now require to determine by the aid of physical science what truth there is in idealism.All is not real that may seem or be declared to be so.The sky is not a vault; color is produced on the visual organism by vibration in a medium; the pleasure is not in the musical sounds.To save realism we are obliged to draw distinctions, say with Aristotle, between common and proper percepts, or with Locke and the Scottish school, between the primary and secondary qualities of matter.But I have a strong conviction that all such distinctions may only be partially correct, and are only provisionally applicable.But as physical and physiological science make farther progress, we may ascertain the exact truth, and find that it clears up many obscure points.As the facts are ascertained, metaphysics should take them up, and, combining our intuitive perceptions with them, may determine precisely what we are entitled to affirm of matter.In the end some of the statements of the Scottish school as to the precise nature of the external reality may be modified or even set aside.But the great truths propounded by such men as Hamilton will only be established, and seen to rest on a basis which can never be moved.It will be acknowledged that there is an external thing independent of mind, and that this is extended, and has a passive potency.However much we may refine it, enough will be left of matter to undermine Berkleianism and every form of idealism.
IV.Metaphysics may be able to give a more accurate expression of fundamental truth.It is one of the peculiar excellencies of the Scottish school that they stand up for first truths which cannot be proven on the one hand nor set aside on the other.They are not just agreed as to the form which they should take, or the language in which they should be expressed.Mr.{460} J.S.Mill and Mr.Herbert Spencer think that they can account for all or many of these by the association of ideas or heredity.But neither of these thinkers is so bold as to maintain that he has done away with all fundamental truth.It can be shown that Mr.Mill is for ever appealing to truths which he assumes and regards himself as entitled to assume.(See " Examination of the Philosophy of J.S.Mill.") Mr.Spencer falls back on a law of necessity which testifies to a great unknown, which he allots as a territory to faith and to religion.I do not admit that he has given a proper expression to the fundamental verity or fundamental verities which he assumes.
He starts on the principle of relativity, as expounded by Hamilton and Mansel, the authoritative metaphysicians when he began to speculate.I do not admit that the known logically or metaphysically implies the unknown.I am sure that his followers will leave behind them as they advance this unknown region of faith.Following out his own method, they will account for it all by circumstances working from generation to generation.But as Mill and Spencer have not been able to get rid of first truths, so no others will and this whether they avow it or no.All processes must conduct to something ultimate.Thought requires a final resting-place, which will be found self-evident, necessary, universal.The age demands that the whole subject be rediscussed, with the view of determining what are the first, the last, and the everlasting principles of thought and truth.Some of those defended by the Scottish metaphysicians may be derivative, but they will be found to imply a root from which they are sprung.{461}