figure, (which may be suggested to the mind by the exercise either of sight or of touch,) is not altogether so obvious; and accordingly it has been the subject of various controversies. To trace the origin of these, and of our other simple notions with respect to the qualities of matter; or, in other words, to describe the occasions on which, by the laws of our nature, they are suggested to the mind, is one of the leading objects of Dr. Reid's inquiry, in his analysis of our external senses; in which he carefully avoids every hypothesis with respect to the inexplicable phenomena of perception and of thought, and confines himself scrupulously to a literal statements of facts. Similar inquiries to these may be proposed, concerning the occasions on which we form the notions of time, of motion, of number, of causation, and an infinite variety of others. Thus, it has been observed by different authors, that every perception of change suggests to the mind the notion of a cause, without which that change could not have happened. Dr. Reid remarks, that, without the faculty of memory, our perceptive powers could never have led us to form the idea of motion. I shall afterwards show, in the sequel of this work, that without the same faculty of memory, we never could have formed the notion of time; and that without the faculty of abstraction, we could not have formed the notion of number.-Such inquiries with respect to the origin of our knowledge, are curious and important; and if conducted with judg ment, they may lead to the most certain conclusions; as they aim at nothing more than to ascertain facts, which, although not obvious to superficial observers, may yet be discovered by patient investigation.

From the remarks which have been just made on our notions of time, of motion, and of number, it is evident that the inquiry concerning the origin of human knowledge cannot possibly be discussed at the commencement of such a work as this; but that it must be resumed in different parts of it, as those faculties of the mind come under our view, with which the formation of our different simple notions is connected.

With respect to the general question, Whether all our knowledge may be ultimately traced from our sensations? I shall only observe at present, that the opinion we form concerning it, is of much less consequence than is commonly supposed. That the mind cannot, without the grossest absurdity, be considered in the light of a receptacle which is gradually furnished from without, by materials introduced by the channel of the senses; nor in that of a tabula rasa upon which copies or resemblances of things external are imprinted; I have already shown at sufficient length. Although, therefore, we should acquiesce in the conclusion, that, without our organs of sense, the mind must have remained destitute of knowledge, this concession could have no tendency whatever to favor the principles of materialism; as it implies nothing more than that the impressions made on our senses by external objects, furnish the occasions on

which the mind, by the laws of its constitution, is led to perceive the qualities of the material world, and to exert all the different modifications of thought of which it is capable.

From the very slight view of the subject, however, which has been already given, it is sufficiently evident, that this doctrine, which refers the origin of all our knowledge to the occasions furnished by sense, must be received with many limitations. That those ideas, which Mr. Locke calls ideas of reflection, (or in other words, the notions which we form of the subjects of our own consciousness,) are not suggested to the mind immediately by the sensations arising from the use of our organs of perception, is granted on all hands; and, therefore, the amount of the doctrine now mentioned, is nothing more than this; that the first occasions on which our various intellectual faculties are exercised, are furnished by the impressions made on our organs of sense; and consequently, that, without these impressions, it would have been impossible for us to arrive at the knowledge of our faculties. Agreeably to this explanation of the doctrine, it may undoubtedly be said with plausibility, (and I am inclined to believe, with truth,) that the occasions on which all our notions are formed, are furnished either immediately or ultimately by sense; but if I am not much mistaken, this is not the meaning which is commonly annexed to the doctrine, either by its advocates or their opponents. One thing at least is obvious, that, in this sense, it does not lead to those consequences which have interested one party of philosophers in its defense, and another in its refutation.

There is another very important consideration which deserves our attention in this argument: that, even on the supposition that certain impressions on our organs of sense are necessary to awaken the mind to a consciousness of its own existence, and to give rise to the exercise of its various faculties; yet all this might have happened without our having any knowledge of the qualities, or even of the existence, of the material world. To facilitate the admission of this proposition, let us suppose a being formed in every other respect like man; but possessed of no senses, excepting those of hearing and smelling. I make choice of these two senses, because it is obvious, that by means of them alone we never could have arrived at the knowledge of the primary qualities of matter, or even of the existence of things external. All that we could possibly have inferred from our occasional sensations of smell and sound, would have been that there existed some unknown cause by which they were produced.

Let us suppose then a particular sensation, to be excited in the mind of such a being. The moment this happens, he must necessarily acquire the knowledge of two facts at once that of the existence of the sensation; and that of his own existence, as a sentient being. After the sensation is at an end, he can remember he felt it; he can conceive that he feels it again. If he has felt a

variety of different sensations, he can compare them together in respect of the pleasure or the pain they have afforded him; and will naturally desire the return of the agreeable sensations, and be afraid of the return of those which were painful. If the sensations of smell and sound are both excited in his mind at the same time, he can attend to either of them he chooses, and withdraw his attention from the other; or he can withdraw his attention from both, and fix it on some sensation he has felt formerly. In this manner, he might be led, merely by sensations existing in his mind, and conveying to him no information concerning matter, to exercise many of his most important faculties; and amidst all these different modifications and operations of his mind, he would feel, with irresistible conviction, that they all belong to one and the same sentient and intelligent being; or, in other words, that they are all modifications and operations of himself. I say nothing, at present, of the various simple notions, (or simple ideas, as they are commonly called,) which would arise in his mind; for example, the ideas of number, of duration, of cause and effect, of personal identity; all of which, though perfectly unlike his sensations, could not fail to be suggested by means of them. Such a being, then, might know all that we know of mind at present; and as his language would be appropriated to mind solely, and not borrowed by analogy from material phenomena, he would even possess important advantages over us in conducting the study of pneumatology.

From these observations it sufficiently appears, what is the real amount of the celebrated doctrine, which refers the origin of all our knowledge to our sensations; and that, even granting it to be true, (which, for my own part, I am disposed to do, in the sense in which I have now explained it,) it would by no means follow from it, that our notions of the operations of mind, nor even many of those notions which are commonly suggested to us, in the first instance, by the perception of external objects, are necessarily subsequent to our knowledge of the qualities, or even of the existence, of matter.

The remarks which I have offered on this doctrine, will not appear superfluous to those who recollect that although it has, for many years past, been a subject of controversy in England, it continues still to be implicitly adopted by the best philosophical writers in France; and that it has been employed by some of them to support the system of materialism; and by others to show, that the intellectual distinctions between man and brutes, arise entirely from the differences in their animal organization, and in their powers of external perception.

CHAPTER II.

OF ATTENTION.

WHEN we are deeply engaged in conversation, or occupied with any speculation that is interesting to the mind, the surrounding objects either do not produce in us the perceptions they are fitted to excite; or these perceptions are instantly forgotten. A clock, for example, may strike in the same room with us, without our being able, next moment, to recollect whether we heard it or not.

In these, and similar cases, I believe, it is commonly taken for granted, that we really do not perceive the external object. From some analogous facts, however, I am inclined to suspect that this opinion is not well founded. A person who falls asleep at church, and is suddenly awaked, is unable to recollect the last words spoken by the preacher; or even to recollect that he was speaking at all. And yet, that sleep does not suspend entirely the powers of perception, may be inferred from this, that if the preacher were to make a sudden pause in his discourse, every person in the congregation who was asleep, would instantly awake. In this case, therefore, it appears, that a person may be conscious of a perception, without being able afterwards to recollect it.

Many other instances of the same general fact might be produced. When we read a book, (especially in a language which is not perfectly familiar to us,) we must perceive successively every different letter, and must afterwards combine these letters into syllables and words, before we comprehend the meaning of a sentence. This process, however, passes through the mind, without leaving any trace in the memory.

It has been proved by optical writers, that, in perceiving the distances of visible objects from the eye, there is a judgment of the understanding antecedent to the perception. In some cases this judgment is founded on a variety of circumstances combined together; the conformation of the organ necessary for distinct vision; the inclination of the optic axes; the distinctness or indistinctness of the minute parts of the object; the distances of the intervening objects from each other, and from the eye; and, perhaps, on other circumstances besides these: and yet, in consequence of our familiarity with such processes from our earliest infancy, the perception seems to be instantaneous; and it requires much reasoning, to convince persons unaccustomed to philosophical speculations, that the fact is otherwise.

Another instance of a still more familiar nature, may be of use, for the farther illustration of the same subject. It is well known

that our thoughts do not succeed each other at random, but according to certain laws of association, which modern philosophers have been at much pains to investigate. It frequently, however, happens, particularly when the mind is animated by conversation, that it makes a sudden transition from one subject to another, which, at first view, appears to be very remote from it; and that it requires a considerable degree of reflection, to enable the person himself by whom the transition was made, to ascertain what were the intermediate ideas. A curious instance of such a sudden transition is mentioned by Hobbes in his Leviathan. "In a company," (says he,) "in which the conversation turned on the civil war, what could be conceived more impertinent, than for a person to ask abruptly, What was the value of a Roman denarius? On a little reflection, however, I was easily able to trace the train of thought which suggested the question for the original subject of discourse naturally introduced the history of the king, and of the treachery of those who surrendered his person to his enemies; this again introduced the treachery of Judas Iscariot, and the sum of money which he received for his reward. And all this train of ideas," says Hobbes, "passed through the mind of the speaker in a twinkling, in consequence of the velocity of thought." It is by no means improbable, that if the speaker himself had been interrogated about the connexion of ideas, which led him aside from the original topic of discourse, he would have found himself, at first, at a loss for an answer.

In the instances which have been last mentioned we have also a proof, that a perception, or an idea, which passes through the mind, without leaving any trace in the memory, may yet serve to introduce other ideas connected with it by the laws of association. Other proofs of this important fact shall be mentioned afterwards.

When a perception or an idea passes through the mind, without our being able to recollect it next moment, the vulgar themselves ascribe our want of memory to a want of attention. Thus, in the instance already mentioned, of the clock, a person, upon observing that the minute hand had just passed twelve, would naturally say, that he did not attend to the clock when it was striking. There seems therefore, to be a certain effort of mind upon which, even in the judgment of the vulgar, memory in some measure depends; and which they distinguish by the name of attention.

The connexion between attention and memory has been remarked

by many authors. "Nec dubium est," (says Quinctilian, speaking of memory,) "quin plurimum in hac parte valeat mentis intentio, et velut acies luminum a prospectu rerum quas intuetur non aversa. The same observation has been made by Locke, and by most of the writers on the subject of education.

But although the connexion between attention and memory has been frequently remarked in general terms, I do not recollect that

* "Memory depends much on attention and repetition."