Meditations - pg. 115

Now I have a passive power of sensation -- of getting and recognising the ideas of sensible objects. But I could never have the use of it if there were not also in existence an active power, either in myself or in something else, to produce or make the ideas. This power certainly cannot exist in me; for it presupposes no action of my intellect, and the ideas are produced without my co-operation, and often against my will. The only remaining possibility is that it inheres in some substance other than myself.