Under the head of perception it may be necessary to remark farther that the term perception (perceptio) is not used in reference to sense without the adjunct sensus or sensuum—the terms in this relation being sensus, sensatio, idea, and the verb sentire not percipere. ↩
The meaning attached to the term “idea” in the writings of Descartes is by no means uniform or constant. The first grand distinction in the signification of the word arises from its application by Descartes to denote indifferently a material or a mental modification; and this in relation to sense and imagination. Considered with respect to these faculties, idea is sometimes applied to designate the impression on the brain or material organism generally, to which the idea proper or mental modification is attached, and at other times to mark the mental modification itself, regarded as the object of the faculty. As instances of the former application of the word, we may adduce the following passages:—“Ideam quam formant hi spiritus.”—Tract. de Homine, § 84. “Glandula ideas objectorum, quae in aliorum sensuum organa agunt, aeque facile recipere possit.”—Ibid. § 85. “Ideas quas sensus externi in phantasiam mittunt.”—Diopt. cap. IV § 6. To obviate the ambiguity incidental to this twofold and quite opposite use of the term, De la Forge, an eminent Cartesian, denominated the movement in the organism species, or corporeal species, reserving idea for the modification of the mind alone.—Traité de Esprit de Homme, chap. X p. 99. Hamilton’s Reid, p. 834.
Descartes himself, indeed, in the course of the controversies to which his speculations gave rise, became aware of the necessity of distinguishing in expression the material from the mental idea; and in order to this he seems occasionally disposed to refuse the appellation idea to the material modification, while he more frequently uses the term image (imago), than idea in this relation. One of these passages I shall quote, not only in proof of this, but also as establishing the fact of the reality and distinctness of the material and mental modifications. “I do not simply (he says) call by the name idea the images that are depicted in the fantasy; on the contrary, I do not call them by this name in so far as they are in the corporeal fantasy; but I designate generally by the term idea all that is in our mind when we conceive a thing in whatever manner we may conceive it.”—Lett. LXXV, Garnier, tom. IV p. 319.
It should be observed, however, that by idea in the sense of corporeal species, Descartes did not mean a picture, likeness, or image of the object existing in the brain, but simply a certain organic movement, or agitation of the nerves, determined by the object and communicated to the brain, the seat of the sensus communis. This purely material modification had, on the one hand, not necessarily any resemblance to the object which was the cause of it, and therefore was not representative of it; nor, on the other, should it be supposed that it in any way resembled, far less was identical with, the (mental) idea connected with it, since notwithstanding certain loose statements, there is sufficient ground to hold that, on the doctrine of Descartes, the corporeal impression was no object of perception or consciousness at all. As these are points of essential importance towards a right comprehension of the philosophy of Descartes, I may be allowed to enter somewhat into detail; and first of all, I shall refer to the passages in which he has distinctly laid down the doctrines here attributed to him.
“That the ideas which the external senses send into the fantasy are not images of the objects; or at least that there is no need of their being like them.
“It must be observed, besides, that the mind does not stand in need of images sent from objects to the brain in order to perceive (as is the generally received opinion of the philosophers); or at least that the nature of these images is to be conceived far otherwise than is commonly done. For, as philosophers consider in them nothing beyond their resemblance to the objects they represent, they are unable to show how these images can be formed by the objects, and received into the organs of the external senses, and finally transmitted by the nerves to the brain. And they had no ground to suppose there were such images, beyond observing that our thought can be efficaciously excited by a picture to conceive the object pictured; from which it appeared to them that the mind must be, in the same way, excited to apprehend the objects which affect the senses, by means of certain small images delineated in our head. Whereas we ought to consider that there are many things besides images that can excite our thoughts; as, for example, words and signs which in no way resemble the things they signify. And if, that we may depart as little as possible from the commonly received opinions, we may be allowed to concede that the
