The subordination of theory to practice is most apparent in the School of Epicurus. It is nearly as clear in the case of the Sceptics, who, denying all possibility of knowledge, left as the only ground of action conviction based on probabilities. Both Schools also agree in considering philosophy as only a means for securing happiness. By the Stoics, on the other hand, the need of philosophic speculation was felt more strongly; but even in their case it may be seen that speculation was not pursued simply for its own sake, but for practical purposes, by which it was also determined. Thus the Stoics, like the Epicureans, in the speculative part of their system confined themselves to current views—thereby showing that the source of their philosophical peculiarities lay elsewhere than in speculation, and that other studies had greater value in their eyes, in which also they considered themselves more proficient. They even expressly stated that the study of nature is only necessary as a help to the study of virtue. It is beyond question, that their chief peculiarities, and those which give them an importance in history, are ethical. The other parts of their system, more particularly those in which their distinctive tenets appear, are likewise regulated by practical considerations. This statement will hereafter be shown in detail. It may suffice to observe now, that the most important point in the logic of the Stoics—the question as to the standard of truth—was decided by a practical postulate; that the fundamental principles of the Stoic metaphysics are only intelligible from the ground of their ethics; that for natural science the Stoics did very little; that in their theory of final causes on which they lay so much stress nature is explained by moral considerations; and that their natural as well as their positive theology bears ample testimony to the practical tone of their system. Standing in advance of the Epicureans by their higher intellectual training and their learned energy, and in opposition to the Sceptics by their dogmatism, the Stoics nevertheless agree with both these Schools in the essentially practical character of their teaching. [(2) Peculiar mode of dealing with the practical problem.]