Hitherto we have been concerned with the speculative branches of knowledge, we have now to turn to practice. Practice, too, is an activity of thought, but an activity which is never satisfied by the process of thinking itself. In practice our thinking is always directed towards the production of some result other than true thought itself. As in engineering it is not enough to find a solution of the problem how to build a bridge over a given river capable of sustaining a given strain, so in directing our thought on the problems of human conduct and the organisation of society we aim at something more than the understanding of human life. In the one case what we aim at is the construction of the bridge; in the other it is the production of goodness in ourselves and our fellow-men, and the establishment of right social relations in the state. Aristotle is careful to insist on this point throughout his whole treatment of moral and social problems. The principal object of his lectures on conduct is not to tell his hearers what goodness is, but to make them good, and similarly it is quite plain that _Politics_ was intended as a text-book for legislators. In close connection with this practical object stands his theory of the kind of truth which must be looked for in ethics and politics. He warns us against expecting precepts which have the exact and universal rigidity of the truths of speculative science. Practical science has to do with the affairs of men’s lives, matters which are highly complex and variable, in a word, with "what may be otherwise." Hence we must be content if we can lay down precepts which hold good in the main, just as in medicine we do not expect to find directions which will effect a cure in all cases, but are content with general directions which require to be adapted to special cases by the experience and judgment of the practitioner. The object of practical science then is to formulate rules which will guide us in obtaining our various ends. Now when we consider these ends we see at once that some are subordinate to others. The manufacture of small-arms may be the end at which their maker aims, but it is to the military man a mere means to _his_ end, which is the effective use of them. Successful use of arms is again the end of the professional soldier, but it is a mere means among others to the statesman. Further, it is the military men who use the arms from whom the manufacturer has to take his directions as to the kind of arms that are wanted, and again it is the statesman to whom the professional soldiers have to look for directions as to when and with what general objects in view they shall fight. So the art which uses the things produced by another art is the superior and directing art; the art which makes the things, the inferior and subordinate art. Hence the supreme practical art is politics, since it is the art which uses the products turned out by all other arts as means to its ends.