In Logic, the Stoic system is noteworthy for their theory as to the test of truth, the _Criterion_. They compared the new-born soul to a sheet of paper ready for writing. Upon this the senses write their impressions (φαντασίαι), and by experience of a number of these the soul unconsciously conceives general notions (κοιναὶ ἔννοιαι) or anticipations (προλήψεις). When the impression was such as to be irresistible it was called (καταληπτικὴ φαντασία) one that holds fast, or as they explained it, one proceeding from truth. Ideas and inferences artificially produced by deduction or the like were tested by this 'holding perception.' Of the Ethical application I have already spoken. The highest good was the virtuous life. Virtue alone is happiness, and vice is unhappiness. Carrying this theory to its extreme, the Stoic said that there could be no gradations between virtue and vice, though of course each has its special manifestations. Moreover, nothing is good but virtue, and nothing but vice is bad. Those outside things which are commonly called good or bad, such as health and sickness, wealth and poverty, pleasure and pain, are to him indifferent (ἀδιάφορα). All these things are merely the sphere in which virtue may act. The ideal Wise Man is sufficient unto himself in all things (αὐταρκής); and knowing these truths, he will be happy even when stretched upon the rack. It is probable that no Stoic claimed for himself that he was this Wise Man, but that each strove after it as an ideal much as the Christian strives after a likeness to Christ. The exaggeration in this statement was, however, so obvious, that the later Stoics were driven to make a further subdivision of things indifferent into what is preferable (προηγμένα) and what is undesirable (ἀποπροηγμένα). They also held that for him who had not attained to the perfect wisdom, certain actions were proper. (καθήκοντα) These were neither virtuous nor vicious, but, like the indifferent things, held a middle place.