It is characteristic of such knowledge that it should be deficient in “exactness,” in precision of statement, and closeness of logical concatenation. We must not look for a mathematics of conduct. The subject-matter of Human Conduct is not governed by necessary and uniform laws. But this does not mean that it is subject to no laws. There are general principles at work in it, and these can be formulated in “rules,” which rules can be systematised or unified. It is all-important to remember that practical or moral rules are only general and always admit of exceptions, and that they arise not from the mere complexity of the facts, but from the liability of the facts to a certain unpredictable variation. At their very best, practical rules state probabilities, not certainties; a relative constancy of connection is all that exists, but it is enough to serve as a guide in life. Aristotle here holds the balance between a misleading hope of reducing the subject-matter of conduct to a few simple rigorous abstract principles, with conclusions necessarily issuing from them, and the view that it is the field of operation of inscrutable forces acting without predictable regularity. He does not pretend to find in it absolute uniformities, or to deduce the details from his principles. Hence, too, he insists on the necessity of experience as the source or test of all that he has to say. Moral experience—the actual possession and exercise of good character—is necessary truly to understand moral principles and profitably to apply them. The mere intellectual apprehension of them is not possible, or if possible, profitless. The _Ethics_ is addressed to students who are presumed both to have enough general education to appreciate these points, and also to have a solid foundation of good habits. More than that is not required for the profitable study of it.