 Reid’s concept of sensation is a main instrument of his opposition to the theory of ideas. He holds sensations to be non-intentional objects of consciousness which have potential to be conceived; they are what they are felt to be and felt to be what they are (Reid 1785 [2002: 36–8, 193–4]). Perceptions, by contrast, are cognitive. An episode of perception breaks down to an act of conceiving an external object and an act of believing in its present existence. Sensations are, then, wholly extrinsic to perceptions. But with one exception, perception of all sorts of objects is attended by a simultaneous sensation which is the effect of the object operating on sensory organs of the perceiver (Reid 1785 [2002:  193–4])[5]