_Remarks of Professor Bowen._--As Professor Bowen has well observed, "The maxim, '_Every event must have a cause_,' is not, like the so-called laws of nature, a mere induction founded on experience, and holding good only until an instance is discovered to the contrary; it is a necessary and immutable truth. It is not derived from observation of natural phenomena, but is super-imposed upon such observation by a necessity of the human intellect. It is not made known through the senses; and its falsity, under any circumstances, is not possible, is not even conceivable. The _cause_ to which it points us, is not to be found in nature. The mere physicist, after vainly searching, ever since the world began, for a single instance of it, has, at length, abandoned the attempt as hopeless, and now confines himself to the mere _description_ of natural phenomena. The _true cause_ of these phenomena must be sought for in the realm, not of _matter_, but of _mind_." _What constitutes Cause._--In this last remark, the author quoted touches upon a question of no little moment. What constitutes a cause? We cannot here enter into the discussion of this question. It is sufficient to remark, that in the ordinary use of the word, as denoting that, but for which a given result will not be, many things beside mind are included as causes. A hammer, or some like instrument, is essential to the driving of a nail. The hammer may be called the cause of the nail being driven; the blow struck by means of the hammer may also be so designated. More properly, the arm which gave the blow, and, more correctly still, the mind which willed the movement of the arm, and not the consequent blow of the hammer, may be said to be the cause. If we seek for _ultimate_ and _efficient_ causes, we must, doubtless, come back to the realm of mind. It is mind that is, in every case, the first mover, the originator of any effect, and it may, therefore, be called the true and prime cause, the cause of causes. _History of the Doctrine._--_Aristotle's View._--The history of the doctrine of causality presents a number of widely different theories, a brief outline of which is all that we can here give. The most ancient division and classification of causes is that of Aristotle, which is based on the following analysis: Every work brought to completion implies four things: an agent by whom it is done, an element or material of which it is wrought, a plan or idea according to which it is fashioned, and an end for which it is produced. Thus, to the production of a statue there must be a statuary, a block of marble, a plan in the mind of the artist, and a motive for the execution of the work. The first of these is termed the _efficient_ cause, the second the _material_ cause, the third the _formal_, and the fourth the _final_ cause. This classification was universally adopted by the scholastic philosophers, and, to some extent, is still prevalent. We still speak of _efficient_ and of _final_ causes.