PART II.

OF THE ORIGIN OF OUR KNOWLEDGE OF FACTS RELATING BOTH TO MIND AND MATTER.

AMONG writers on the science of mind, there was formerly much controversy in regard to the origin of our ideas. Some maintained that they are derived entirely from perception, that is, through the external senses; others considered them as arising partly from perception and partly from consciousness, or reflection; and some added a third class, which they called innate ideas, and which were supposed to exist in the mind itself, independently of and prior to the exercise either of perception or reflection. This phraseology had its origin in the ancient theory of ideas, according to which something was supposed to exist distinct both from the mind and the external object of its perception. This, as we have formerly seen, was what philosophers meant by an idea. It was believed to be the immediate object of the mind's perception, but to be only a kind of image or representative of the object perceived. This hypothesis, which kept its place in the science of mind till a very recent period, is now generally admitted to have been a fiction of philosophers; and the phraseology respecting ideas is abandoned by the best practical writers; because, though the ancient doctrine be exploded, and the term may be used only in a figurative sense, it still seems to imply something existing in the mind distinct from the mind itself. The impressions derived from external things are therefore to be considered as the occasions on which the various powers of the mind are brought into action. These powers themselves then become the objects of consciousness or reflection, and by their further exercise we acquire certain notions which arise out of the mental operations. This doctrine gives no encouragement to the scheme of materialism, for it is clear that we cannot remember till we are furnish

Different opinions. Ancient theory of ideas-what? Present opinion of this theory Modern view-what?

ed with some fact to be remembered; but this can never be supposed to affect our belief in the existence of the pow er of memory before the fact was so furnished. If we could suppose the case of a man who had lived all his life in the dark, he certainly could not see, but we should not say that the admission of light imparted to him the power of vision; it only furnished the circumstances which gave occasion to the exercise of sight. It has accordingly been shown by Mr. Stewart, that though we may not be conscious of our mental powers till they are called into action, yet this may arise from the most simple sensation, such as affords no evidence of the properties, or even of the existence of the material world.

Through the senses, then, we acquire a knowledge of the facts relating to external things. The mental processes thus brought into action then become the subjects of consciousness, and we acquire a knowledge of the facts relating to them. By a further exercise of these powers on various facts referring to both matter and mind, we acquire certain notions arising out of our reflection upon the relations of these facts, such as our notions of time, motion, number, cause and effect, and personal identity; and we acquire, further, the impression of certain fundamental laws of belief, which are not referable to any process of reasoning, but are to be considered as a part of our constitution, or a spontaneous and instinctive exercise of reason in every sound mind.

The origin of our knowledge then is referable, in a philosophical point of view, to perception and reflection. But, in point of fact, the knowledge which is acquired by an individual through his own perception and reflection is but a small part of what he possesses; much of the knowledge possessed by every one is acquired through the perceptions of other men. In an essay, therefore, which is intended to be entirely practical, I shall include this last department under the head of Testimony. The division of this part of the subject will therefore be,

1. Sensation and Perception.

2. Consciousness and Reflection.

3. Testimony.

Illustration. Knowledge of external things-how acquired? Of their relations? Two sources? Additional source. Summary.

SECTION I.

OF SENSATION AND PERCEPTION.

We know nothing of perception except the fact that cortain impressions made upon the organs of sense convey to the mind a knowledge of the properties of external things. Some of the older speculations on this subject have already been referred to. In these the mind was compared to a camera obscura, and the transmission of the forms or images of things to it from the organs of sense was explained by the motion of the animal spirits, or the nervous fluid, or by vibrations in the substance of the nerves. All such speculations are now dismissed from the investigation, being considered as attempts to penetrate into mysteries which are beyond the reach of the human faculties, and consequently not the legitimate objects of a philosophical inquiry.

Our first knowledge of the existence and properties of the material world is evidently of a complex nature. It seems to arise from the combined action of several senses, conveying to us the general notion of certain essences which are solid and extended, or possessed of those properties which characterize material things. Without this general knowledge previously acquired, our various senses acting individually could convey to us no definite notion of the properties of external things. A smell, that is, a mere odor, for example, might be perceived by us, but would convey nothing more than the sensation simply. It could not communicate the impression of this being a property of an external body, until we had previously acquired a knowledge of the existence of that body, and had come by observation to associate the sensation with the body from which it proceeds. The same holds true of the other senses; and we are thus led at the very first step of our inquiry to a complicated process of mind without which our mere sensations could convey to us no definite knowledge.

Having thus acquired a knowledge of the existence and

Former theories. How now considered? First knowledge-how obtained? Succeeding steps-what?

general properties of material things, we next derive from our various senses a knowledge of their more minute characters. These are generally divided into primary and secondary. The primary qualities of material things are such as are essential, and must at all times belong to matter; such as solidity and extension. These properties necessarily convey to us a conviction of something existing out of the mind, and distinct from its own sensations. The secondary qualities, again, are color, temperature, smell, taste, &c. These are not essential properties of matter, but qualities producing sensations in a sentient being; they may or they may not belong to any particular body, or they may be attached to it at one time and not at another. Hence they convey to us primarily no definite notion in regard to the existence or properties of external things, except, as Mr. Stewart expresses it, "as the unknown cause of a known sensation." One of the quibbles or paradoxes of the scholastic philosophy was, denying the real existence of these secondary qualities of matter. Every one is familiar with the humorous account given in the "Guardian" of the attainments of a youth from college, and his display of them when on a visit to lady Lizard, his mother. "When the girls were sorting a set of knots he would demonstrate to them that all the ribands were of the same color, or rather of no color at all. My lady Lizard herself, though she was not a little pleased with her son's improvement, was one day almost angry with him; for, having accidentally burnt her fingers as she was lighting the lamp for her teapot, in the midst of her anguish Jack laid hold of the opportunity to instruct her that there is no such thing as heat in the fire." Such speculations, which were at one time common in the schools of philosophy, had their origin wholly in an abuse of terms. The term heat, for

example, has two meanings, which are quite distinct from each other. It means a sensation produced in a sentient -being, and in this sense it may be said with truth that there is no heat in fire; but it means also a quality in material substances capable of producing this sensation, and it is in this sense that we speak of heat as a property of matter.

Classification of qualities. Definitions. Extract given in the Guardian.

Notwithstanding this explanation of the different senses in which the word heat is used, many persons find it difficult to understand that there is any sense in which it can be said with truth that there is no heat in fire. But a little reflection will make it plain.

If a man puts his hand among coals he feels a burning, painful sensation, which we call heat. Now when it is said there is no heat in fire, the meaning is that there is no such burning, painful sensation. And certainly no one can suppose that there is. There cannot be suffering in the fire, or even any feeling of warmth, or sensation of any kind; and it is in this sense alone that the word is used, when the existence of heat in the fire is denied. So with all the other secondary qualities. Smells, tastes, sounds, &c. are all feelings in us. ternal objects themselves cannot have these feelings, or any other. They have some peculiarity or property which excites these feelings in us, but not the feelings or sensations themselves.

The ex

The process by which we acquire a knowledge of external things is usually divided into two stages, namely, sensation and perception; the former implying the corporeal, the latter the mental part of it. Others apply the term perception to both; and, according to Dr. Brown, sensation is the simple impression made upon the organs of sense; perception is an association formed between this impression and an external substance which we have ascertained to be

concerned in producing it. Our senses, by which this knowledge is acquired, are generally reckoned five,—viz: sight, hearing, taste, smell, and touch. Dr. Brown proposes to add our muscular frame, and apparently with good reason; for there seems ground for believing that it is by resistance to muscular action that we acquire the notion of solidity, and that this could not be acquired by touch alone.

Our first impression of the existence and solidity of material objects, then, seems to be derived from touch combined with muscular resistance; and at the same time we acquire the knowledge of temperature, roughness or smoothness, &c. There has been some difference of opinion in regard to the manner in which we acquire the notion of extension, including figure and magnitude. It is evident that it cannot be acquired from touch alone; but it may be acquired from touch combined with muscular motion, as when we move the hand over the surface of a body. This, how ever, includés also the idea of time,-for our notion of the extent of a surface when the hand moves over it is very

Explanation. Secondary qualities; their nature? Distinction between sensation and perception. Number of the senses. First notions-how obtained?

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