In his moral theory Cicero shows greater decision. He is unwavering in his repudiation of the Epicurean view that virtue and pleasure are one, [67] and generally adheres to that of the other schools, who here agree in declaring that virtue consists in following nature. [68] But here occurs the difficulty as to what place is to be assigned to external goods. At one time he inclines to the lofty view of the Stoic that virtue is in itself sufficient for happiness; at another, struck by its inapplicability to practical life, he thinks this less true than the Peripatetic theory, which takes account of external circumstances, and though considering them as inappreciable when weighed in the balance against virtue, nevertheless admits that within certain limits they are necessary to a complete life. Thus it appears that both in physics and morals he doubted the reality of the great abstract conceptions of reason, and came back to the presentations of sense as at all events the most indisputably probable. This would lead us to infer that he rested upon the senses as the ultimate criterion of truth. But if he adopts them as a criterion at all, he does so with great reservations. He allows the senses indeed the power of judging between sweet and bitter, near and distant, and the like, but he never allows them to determine what is good and what is evil. [69] And similarly he allows the intellect the power of judgment on genera and species, but he does not deny that it sometimes spins out problems which it is wholly unable to solve. [70] Since therefore neither the senses nor the intellect are capable of supplying an infallible criterion, we must reject the Stoic doctrine that there are certain sensations so forcible as to produce an irresistible conviction of their truth. For these philosophers ascribe the full possession of this conviction to the sage alone, and he is not, nor can he be, one of the generality of mankind. Hence Cicero, who writes for these, gives his opinion that there are certain sensuous impressions in which from their permanence and force a man may safely trust, though he cannot assert them to be absolutely true. [71] This liberal and popular doctrine he is aware will be undermined by the absolute scepticism of the New Academy; [72] but he is willing to risk this, and to put his view forward as the best possible approximation to truth.