In De Somno et Vigilia 2 Aristotle observes that sleep and waking are contrary states which simultaneously affect all individual senses of an animal. Aristotle argues that this occurs because there is a common sense organ which controls the peripheral sense organs in such a way that the peripheral sense organs are active or incapacitated depending on whether the common sense organ is active or incapacitated. Aristotle's argument seems to allow for the conclusion that the common sense, which is located in the common sense organ, controls the individual senses located in the peripheral sense organs. In the course of his argument Aristotle appeals to some ‘common power’ which accompanies all the senses. This power enables one to perceive that one is seeing and hearing, and to discriminate between heterogeneous special perceptibles. This chapter investigates what ‘perceiving that one is seeing and hearing’ amounts to. It is shown that perceiving that one is seeing and hearing refers to the awareness of the activity of one's own senses. This awareness characterizes the state of waking, just as its absence characterizes the state of sleep. It is argued that the ‘common power’ which enables one to be aware of the activity of one's senses is the higher-order perceptual power, i.e. the common sense. However, this conclusion has to be aligned with Aristotle's argument in De Anima III.2 in which he seems to claim that we perceive that we see by nothing other than sight, and in which he does not mention any higher-order powers or capacities.
Keywords: De Somno et Vigilia, De Anima, waking, sleep, control, consciousness, activity, common sense organ, peripheral sense organs