Sidebilder
PDF
ePub

been refuted upon his principles, and moreover, that no discovery of importance has been made since his time; and if we wish that the science of the human mind should be cul. tivated with advantage, we must commence in it at the point in which he terminated, and erect our superstructure upon his foundation. These assertions we trust we shall be able to prove by satisfactory arguments.

CHAPTER ITI.

power and

Of Perception. The first in order of the phenomena of the human mind, is perception; by which term is meant that power, by means of which we hold converse with the external world, and the operations of our own minds. Perception, like almost all terms of a similar nature, sometimes denotes the sometimes the acts of that power, by which we discern the external and internal objects of contemplation. It is a generick term, including two species under it, sensation and reflection; sensation, by which we become acquainted with the qualities and operations of the exterior world, and reflection or consciousness, by which we become acquainted with the properties and operations of our own minds. We are said to have perceptions of colour, figure, motion, hardness, and in like manner of thinking, doubting, hoping, believing and fearing, which are acts of the mind. By sensation, we obtain our ideas of all the primary and secondary qualities of body: the first of which are figure, hardness, extension, motion, rest; and the second, colour, heat, cold, sweetness, sound and such like. By primary qualities Des Cartes and Locke mean those which belong to bodies, whether we perceive them or not; by secondary those which cannot properly be said to be in the bodies themselves, but are only sensations in us excited by certain powers existing in exterior objects. Sensation and reflection, therefore, according to Mr. Locke, who may be considered as the original author of this theory, since none of the philosophers who preceded him appear to have had any distinct knowledge of it, are the two great and sole inlets of human knowledge. Through these

two channels we obtain all our simple ideas, which are the elementary principles out of which the busy and curious mind of man forms an endless diversity of combinations. As to the process, by which ideas of the external world are excited in us, Mr. Locke says very little; but as the faithful Interpreter of nature, whose province is to trace her secret operations, as far as the limited faculties bestowed upon our race admit, he maintains, that those ideas can be produced in us only by impulse or the action of outward objects upon the senses: as in taste, by the actual contact of sapid substances with the tongue and palate, in smelling the odorous effluvia emitted from substances striking upon the nostril, in hearing, the vibrations of air upon the ear, and in seeing, the impinging of the rays of light, that pass from the object upon the retina of the eye. How it happens that this action upon the outward organ, occasions perception in any case; that the formation of an image upon the retina, for instance, renders objects visible to us, is considered by the most profound philosophers, as utterly unsearchable to the human mind, Facts without number may be adduced to show, that in order to distinct vision, an image must be formed upon the retina, and moreover, that the action produced in the nervous coat at the bottom of the eye must be communicated by the nerves leading to the brain, to that membrane, usually regarded as the common sensorium. So far the doctrine of philosophers is substantiated by experiment and observation. For, if from any cause, as a disorder in the membranes of the eye or any discoloration of its humours, no distinct image be thrown upon the retina, or if from any defect in the system of nerves leading from the bottom of the eye to the brain, the necessary motion, or action, to be transmitted to the common sensorium be intercepted, the object is not perceived.

Further than this, however, a sound philosophy does not pretend to conduct us into the mysteries of nature. Whether the action produced in the nervous coat be longitudinal or vibratory, how it happens that any motions excited in a system of nerves should produce ideas in our minds, or what is the nature of our ideas; no philosophers, who have just conceptions of the limited sphere of human knowledge, have ever undertaken to determine. Such disquisitions were reserved solely to exercise the ingenuity and excite the literary hostilities of the Schoolmen, who in their contests with each other, entirely lost sight of nature, and were contented with gaining the palm of victory, by the dexterous employment of learned terms, to which they themselves annexed no precise meanings.

Having thus briefly stated the principles of Mr. Locke and the Philosophers, the task which now devolves upon us is to vindicate this system from the objections which have been alledged against it by Dr. Reid. This author admits that we perceive no external object but by means of certain bodily organs God has given us for that purpose.” This he could not deny; since it is incontrovertibly proved by the fact, that a man borr blind can have no ideas of colour, one deprived of hearing has no ideas of sounds, and that the same result takes place in case of a deficiency in the other senses; there is a want of that train of ideas introduced by them. He allows also, that “there is sufficient reason to conclude, that in perception the object produces some change in the organ; the organ produces some change upon the nerve; and the nerve produces some change in the brain.” In these particulars he exactly agrees with Mr. Locke and the Philosophers. But the first point in their doctrine which he thinks objectionable; and upon account of which he srparates from them, is, that “ without good reason, they have concluded that the impressions made upon the body are the proper efficient cause of perception.” “Some Philosophers,” he continues, “ among

« ForrigeFortsett »