3. If we contemplate the whole field of human knowledge, attained or attainable, we find that it separates itself obviously, and as it were spontaneously, into two divisions, which stand so strikingly in opposition and contradistinction to one another, that in all classifications of our knowledge they have been kept apart. These are, _physical_ science, and _moral_ or psychological science. The difference between these two departments of our knowledge does not reside in the subject-matter with which they are conversant: for although, of the simplest and most elementary parts of each, it may be said, with an approach to truth, that they are concerned with different subject- matters--namely, the one with the human mind, the other with all things whatever except the mind; this distinction does not hold between the higher regions of the two. Take the science of politics, for instance, or that of law: who will say that these are physical sciences? and yet is it not obvious that they are conversant fully as much with matter as with mind? Take, again, the theory of music, of painting, of any other of the fine arts, and who will venture to pronounce that the facts they are conversant with belong either wholly to the class of matter, or wholly to that of mind? The following seems to be the _rationale_ of the distinction between physical and moral science. In all the intercourse of man with nature, whether we consider him as acting upon it, or as receiving impressions from it, the effect or phenomenon depends upon causes of two kinds: the properties of the object acting, and those of the object acted upon. Everything which can possibly happen in which man and external things, are jointly concerned, results from the joint operation of a law or laws of matter, and a law or laws of the human mind. Thus the production of corn by human labour is the result of a law of mind, and many laws of matter. The laws of matter are those properties of the soil and of vegetable life which cause the seed to germinate in the ground, and those properties of the human body which render food necessary to its support. The law of mind is, that man desires to possess subsistence, and consequently wills the necessary means of procuring it. Laws of mind and laws of matter are so dissimilar in their nature, that it would be contrary to all principles of rational arrangement to mix them up as part of the same study. In all scientific methods, therefore, they are placed apart. Any compound effect or phenomenon which depends both on the properties of matter and on those of mind, may thus become the subject of two completely distinct sciences, or branches of science; one, treating of the phenomenon in so far as it depends upon the laws of matter only; the other treating of it in so far as it depends upon the laws of mind.