Stoicism, but which by the progress of architectural skill has since then been made less damaging, science is like a firm and immoveable building constructed upon a shifting foundation[78]. Finally ordinary men can reach comprehension, but only the wise man can attain to science[79]. [Sidenote: The criterion reviewed.] =157.= We revert to the difficult problem of the criterion of truth, that is, the discovery of a rule by which the true can separated from the false. Our authorities differ greatly as to what the Stoic criterion is; and this vacillation must have placed the Stoics at a great disadvantage in their controversy with the Academics, who maintain that there is no criterion. The most usual statement is that the ‘comprehensive mind-picture’ (καταληπτικὴ φαντασία) is the criterion; this view is expressly attributed to Chrysippus, Antipater, and Apollodorus[80]. As we have seen, the meaning of this is that a true mind-picture can be distinguished from one that is false by the note of clearness, and this general doctrine can be traced back to Zeno[81]. It appears at first sight to provide a criterion which can be applied by the percipient at the moment when it is needed, and it was doubtless intended to be a practical tool in this sense; but under the pressure of criticism the Stoics were frequently compelled to modify it. They could not but admit that in the case of dreams and drunken visions it is only at a later moment that the lack of clearness can be appreciated[82]; whereas on the other hand a picture may be perfectly clear, and yet the percipient, because of some prepossession, may not realize this. Such was the case when Hercules brought Alcestis from the world below; her husband Admetus received a true mind-picture of her, but put no confidence in it, because he knew her to be dead. It follows that no mind-picture can be implicitly trusted for itself; for our sense organs may be clouded, or our previous experience in conflict with it. If the Academics urged that the sure note of clearness is not to be found in the senses[83], the Stoics admitted as much when they now said that a true comprehensive picture must come from a real object[84], when they added the words that ‘no objection must arise[85]’; thus really admitting that it must be not only persuasive, but also such as no reasoning process can shake, and such as has been examined from all sides[86]. Thus they shifted the centre of certainty from the single comprehension to the general field of science; they still held to it in theory, but no longer maintained its practical application. For this too they had the authority of the older masters. For we learn on the authority of Posidonius that ‘some of the older Stoics’ held the true criterion to be ‘right reason’ (ὀρθὸς λόγος)[87], and this is equivalent to saying that only the deity and the wise man possess the secret[88]. In a loose sense any important part of the Stoic theory of reason may be