  Plato’s Protagoras, which greatly influenced the Stoics, can help us here. This text contrasts the power of phantasia (often translated ‘appearance’) with an art of measurement, the former often going wrong because comparative or perspectival (A looks tall because she’s beside the very short B; B looks taller than A because she’s closer to me), and standing in need of correction by an unchanging standard (a meter ruler, for example) (356b–57a). That Marcus may find the same defects of perspective in impressions is suggested indirectly by the corrections he prescribes: inspect your impressions (ii.7, iii.6, v.22, viii.13, viii.26); test them by ‘physicizing, ethicizing, dialecticizing’ (viii.13), that is to say, by seeing how they fare when tested against your physical, ethical, and dialectical understanding—all of which are informed by a picture of the whole. In xii.18, he tells himself: