=147.= In order then that we may distinguish the true mind-picture from the false, we have need of a ‘rule’ (κανών) or ‘criterion’ (κριτήριον). The true mind-picture is a stirring of the soul, which reveals both what is taking place in the soul and the object which has caused this: just as light reveals both itself and the objects that lie within its range[25]. On the other hand the false mind-picture is an empty twitching of a soul which is not in a healthy condition[26]; no real object corresponds to it, but to that which appears to be an object corresponding to it we give the name ‘phantasm[27].’ When Orestes thinks he sees the Furies leaping upon him, though his sister assures him that in real truth he sees nothing, the vision of the Furies is a phantasm. The appearances of dreams are equally phantasms[28]. Now a true mind-picture differs from that of a phantasm by being clearer; or, in other words, the distinctive note of a true mind-picture is its ‘clearness’ (ἐνάργεια, _perspicuitas_)[29]. Clearness then is a quality which attaches itself to a true vision in a way in which it can never attach itself to a work of phantasy[30]. To this clearness the mind cannot but bow[31]; it is therefore (so far as our study has proceeded) the criterion of truth[32]. [Sidenote: Assent.] =148.= The mind-picture as such is not within a man’s control; but it rests with him to decide whether he will give it his ‘assent’ (συγκατάθεσις, _adsensio_ or _adsensus_)[33]. This assent is therefore an act of the soul, in its capacity as will; and can only be rightly exercised by a soul properly strung, that is, possessed of due tension. Assent wrongly given leads to ‘opinion’ (δόξα, _opinio_), and all wrong assent is error or ‘sin’ (ἁμαρτία, _peccatum_). This error may take place in two directions, either by a hasty movement of the will (προπίπτειν), giving assent to a picture which is not really clear; or by feebleness of will, which leads to assent in a false direction (διαψεύδεσθαι)[34]. Even haste however is a form of weakness, so that we may say that all opining is a weak form of assent[35]. To ensure a right assent due attention should be given to each of its parts; it includes (i) the intention of mastering the object (πρόθεσις); (ii) careful attention directed to the object, or ‘application’ (ἐπιβολή); and (iii) assent in the narrower sense[36]. Apart from assent, three courses remain open: these are (i) ‘quiescence’ (ἡσυχάζειν, _quiescere_): (ii) ‘suspense of judgment’ (ἐπέχειν, _adsensum sustinere)_, which is a settled quiescence; and (iii) negation[37]. [Sidenote: Comprehension.]