We must take care not to assume - as our philosophers [i.e. the scholastics] commonly do - that in order to have sensory awareness the soul must contemplate certain images [i.e. the species] transmitted by objects to the brain; or at any rate we must conceive the nature of these images in an entirely different manner from that of the philosophers. For since their conception of the images is confined to the requirement that they should resemble the objects they represent, the philosophers cannot possibly show us how the images can be formed by the objects, or how they can be received by the external sense organs and transmitted by the nerves to the brain. Their sole reason for positing such images was that they saw how easily a picture can stimulate our mind to conceive the objects depicted in it, and so it seemed to them that the mind must be stimulated to conceive the objects that affect our senses in the same way - that is, by a little picture formed in our head. We should, however, recall that our mind can be stimulated by many things other than images - by signs and words, for example, which in no way resemble the things they signify. And if, in order to depart as little as possible from accepted views, we prefer to maintain that the objects we perceive by our senses really send images of themselves to the inside of our brain, we must at least observe that in no case does an image have to resemble the object it represents in all respects, for otherwise there would be no distinction between the object and its image. It is enough that the image resembles its object in a few respects. Indeed the perfection of an image often depends on its not resembling its object as much as it might. You can see this in the case of engravings: consisting simply of a little ink placed here and there on a piece of paper, they represent to us forests, towns, people, and even battles and storms; and although they make us think of countless different qualities in these objects, it is only in respect of shape that there is any real resemblance. And even this resemblance is very imperfect, since engravings represent to us bodies of varying relief and depth on a surface which is entirely flat. Moreover, in accordance with the rules of perspective they often represent circles by ovals better than by other circles ... and similarly for other shapes ... Now we must think of the images formed in our brain in the same way, and note that the problem is to know simply how they can enable the soul to have sensory awareness of all the various qualities to which they correspond - not to know how they can resemble these objects. (Descartes, Optics, Discourse IV, CSM translation [emphasis added])
Discourse V begins, "You see, then, that in order to have sensory awareness the soul does not need to contemplate any images resembling the things which it perceives."
Berkeley was certainly familiar with Descartes' Optics - it is one of the principal targets he has in view in the New Theory of Vision, and he cites it multiple times. It seems not unlikely that this passage, especially the portions I have bolded, could have directly inspired Berkeley's own work on the subject. On Berkeley's view, the case of visual stimuli (and, as it turns out, all sense data) literally is the case of "signs and words ... which in no way resemble the things they signify."Posted by Kenny at September 18, 2009 4:34 PM
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