By the laws of mind (i.e. as considered in this treatise, the laws of mental phenomena) are meant the laws according to which one state of mind is produced by another. If M. Comte and others be right in saying that, in like manner with the mental phenomena called sensations, all the other states of mind have for their proximate causes nervous states, there would be no original laws of mind, and Psychology would be a mere branch of Physiology. But at present, this tenet is not proved, however highly probable; and, at all events, the characteristics of those nervous states are quite unknown; consequently the uniformities of succession among the mental phenomena, which undoubtedly do exist, and which are not proved to result from more general laws, must be considered as the subject of a distinct science called Psychology. We can ascertain only by experiment the simple laws of Mind, such as--1. That a state of consciousness can be reproduced in the absence of the cause which first excited it (i.e. that every mental impression has its idea), and--2. That these secondary mental states themselves are produced according to the three laws of ideas. But the complex laws are got from these simple laws, according either to the Composition of Causes, when the complex idea is said to _consist of_ the Simple Ideas, or to chemical combination, when it is said to be _generated by_ them. Hartley and Mr. James Mill indeed hold _all_ the mental phenomena to be generated by chemical combination from simple ideas of _sensation_, however unlike to the alleged results; but even though they had proved their theory, employing the Method of Difference, and not only the Method of Agreement (which latter itself they have used only partially), we should still have to study the complex ideas themselves inductively, before we could ascertain their sequences. The analytical enquiry (neglected alike by the German metaphysical school, and by M. Comte) into the general laws of mind, will show that the mental differences of individuals are not ultimate facts, but may be referred generally to their particular mental history, their education and circumstances, but sometimes also to organic differences influencing the mental phenomena, not directly, but through the medium of the psychological causes of the latter. Men's animal instincts, however, are probably, equally with the mere sensations, connected directly with physical conditions of the brain and nerves. Whether or not there be any direct relation between organic causes and any other mental phenomena, Physiology is likely in time to show; but at least Phrenology does not embody the principles of the relation. CHAPTER V. ETHOLOGY, OR THE SCIENCE OF THE FORMATION OF CHARACTER.