Version: v1, Published online: 1998
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2. Perception and sensation
Reid attacks the view of David Hume that nothing can ever be present to the mind but an image or perception and that the senses are only inlets through which these images are conveyed. According to Hume, the table which we see, and which appears to diminish as we move further from it, is not the real table that exists independently of us and undergoes no alteration as we move away from it; it is the image of the table that is immediately present to the mind, or seen. Reid claims that we have no good grounds for accepting the existence of such images or ideas, arguing that in perceiving something the mind has an immediate acquaintance with it. Perception of an external object involves some conception or notion of the object and an irresistible conviction of its present existence; the conviction is immediate and not inferential (1785: II.v).
But consider smelling a rose and the agreeable sensation raised when the rose is smelled. Reid allows that he is led, by his nature, to conclude some quality to be in the rose, which is the cause of this sensation. However in sensation there is no object distinct from the act of mind as there is in the cases of perception and memory; in ‘I feel pain’ the distinction between act and object is merely grammatical. Moreover the firm cohesion of the parts of a body is quite unlike that sensation by which I perceive it to be hard. And so sensations are not suitable as bases for inferences to qualities in objects. Given this firm rejection of the doctrine that we can have no conception of any material thing which is not like some sensation, it is hard to see how sensations can be more than occasional causes of conceptions. Reid even raises doubts about the existence of sensations in certain cases of perception (1764: VI). Thus there is no sensation for what he calls visible figure. The different positions on a visually perceived body facing an observer make a two-dimensional figure with length and breadth only. This visible figure represents the three-dimensional form of the perceived body which has length, breadth and thickness.
Sensation is an important ingredient of Reid’s distinction between primary and secondary qualities. He states that our senses give us a direct and distinct notion of the primary qualities of objects, in spite of the obstacles mentioned above, but only a relative and obscure notion of secondary qualities: they are unknown qualities that produce certain sensations in us. Yet Reid freely admits (1785: II.xviii) that in seeing a coloured body the sensation is indifferent, drawing no attention, and that the (unknown) quality which we call its colour is the only object of our attention. Presumably we should follow Reid in distinguishing between the colour of a body, conceived to be a fixed and permanent quality in the body, and the appearance of colour to the eye which may be varied in a thousand ways, while not following him in his view that it is the former that we attend to when we look at a coloured object.
Reid thinks there is no visual perception of spherical objects without perception of their visible figure and colour; these are all that is originally perceived by sight even though we learn to perceive by the eye almost anything, including sphericality, that we can originally perceive by touch. It should be clear that this Berkelian view of vision sits uncomfortably with Reid’s position that perception of something includes an immediate conviction of its present existence, even though it enables him to dismiss many cases of fallacy of vision as rash inferences.
Reid does not deny that there is no perception unless some impression is made upon the organ of sense either directly or through a medium which is then communicated to the nerves and by them to the brain (1785: II). However, he insists upon the following points. First, there is nothing more ridiculous than to imagine that any motion or modification of matter should produce thought. Second, when I look upon the wall of my room the wall does not act at all and is incapable of action; rather the perceiving of it is an act or operation in me, albeit an involuntary one.
Gallie, Roger. Perception and sensation. Reid, Thomas (1710–1796), 1998, doi:10.4324/9780415249126-DB059-1. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/biographical/reid-thomas-1710-1796/v-1/sections/perception-and-sensation.
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