In Pl. Tht. 182c1-183b5 Socrates deals with the implications of the Heraclitean doctrine of flux for the thesis (attributed to Protagoras) that knowledge is perception. After having illustrated that, according to the flux theory, the perceived object is subject to constant change (182d1-5), he deals with perception itself (182e1-2): μενειν ποτε εν αυτω τω οραν η ακουειν. It is generally believed that this phrase means that sight, for instance, does not remain within the domain of sight, but changes into another kind of perception. Thus the words εν αυτω τω οραν η ακουειν are taken as an obligatory constituent belonging to μενειν; the whole phrase is supposed to mean, 'Shall we say that it ever stays in the condition of seeing or hearing?' (Sedley). This contribution shows why this interpretation is untenable. As an alternative, it is argued that μενειν is used absolutely as 'remain as one was'; the phrase εν αυτω τω οραν η ακουειν serves to indicate that a perception, while constantly changing, does remain within its own domain; that is, sight is never stable, but it does remain within the domain of sight. The whole sentence means, 'Does it ever remain the same within sight or hearing itself?'