=77.= The chief cause of error, Zeno found, lay in hasty assertion; and this he held was a fault not so much of the intellect as of the will. In the simplest case the senses present to the mind a ‘picture’ (φαντασία, _visum_), carrying with it the suggestion of a statement (e.g. ‘that is a horse’). But it is for the man to consider well whether this suggestion is true, and only to give his ‘assent’ (συγκατάθεσις, _adsensus_) when he is so assured. Assent is an act of the will, and therefore in our power. Of a picture to which he has given his assent the wise man should retain a firm hold; it then becomes an item of ‘comprehension’ (φαντασία καταληπτική, _comprehensio_), and may be stored in the memory, thus preparing the way for further acquisitions of knowledge, which in the end combine in ‘scientific knowledge’ (ἐπιστήμη, _scientia_). This theory is little more than an exhortation against the prevailing error of hasty thought (δόξα, _opinio_); but it made a very deep impression, especially as enforced by Zeno’s gestures. He stretched out his fingers and shewed the open palm, saying ‘Such is a picture.’ He partially contracted his fingers, and said ‘This is assent.’ Making a closed fist, he said ‘This is comprehension.’ Then closing in the left hand over the right he pressed his fist tight, and said ‘This is science, and only the wise man can attain to it[45].’ We have no reason to suppose that this theory was in any way suggested by Stilpo, from whom however Zeno probably learnt to attach importance to the formal part of reasoning, such as ‘definition’ and the use of the syllogism. With Stilpo he shared an aversion to the Platonic theory of ideas, maintaining that ideas are by no means realities but have only a ‘kind of existence’ in our minds, or (as we should call it to-day) a ‘subjective existence[46].’ [Sidenote: Zeno studies under Polemo.]