III. CHA P. friend, in order to draw his picture, he believes for the moment that his friend is before him. The belief, indeed, is only momentary; for it is extremely difficult, in our waking hours, to keep up a fteady and undivided attention to any object we conceive or imagine; and, as foon as the conception or the imagination is over, the belief which attended it is at an end. We find that we can recal and dismiss the objects of these powers at pleasure; and therefore we learn to confider them as creations of the mind, which have no feparate and independent existence. THE Compatibility of fuch a fpeculative disbelief, as I have here supposed, of the existence of an object, with a contrary momentary belief, may perhaps be more readily admitted, if the following experiment be confidered with attention. "philofophy convinced him, that he was in no more danger in the dark when "alone, than with company. Here an unreasonable belief, which was merely "a prejudice of the nursery, ftuck fo faft as to govern his conduct, in oppo"fition to his fpeculative belief as a philofopher, and a man of sense." "There are few perfons who can look down from the battlement of a very "high tower without fear; while their reafon convinces them, that they are in "no more danger than when standing upon the ground." These facts are easily explicable, on the fuppofition, that whenever the objects of imagination engrofs the attention wholly, (which they may do, in oppofition to any fpeculative opinion with refpect to their non-existence,) they produce a temporary belief of their reality. Indeed, in the last paffage, Dr. Reid seems to admit this to be the cafe; for, to fay that a man who has a dread of apparitions, believes himself to be in danger when left alone in the dark, is to fay, in other words, that he believes (for the time) that the objects of his imagination are real. SUPPOSE may be feen between the III. SUPPOSE a lighted candle to be fo, placed before a concave CHA P. mirror, that the image of the flame mirror and the eye of the obferver. is acquainted with the principles of optics, or who has feen the experiment made before, has so strong a fpeculative conviction of the non-existence of the object in that place where he sees its image, that he would not hesitate to put his finger to the apparent flame, without any apprehenfion of injury. SUPPOSE, however, that in fuch a cafe it were poffible for the observer to banish completely from his thoughts all the circumstances of the experiment, and to confine his attention wholly to his perception; would he not believe the image to be a reality; and would he not expect the fame confequences from touching it, as from touching a real body in a state of inflammation? If these questions be answered in the affirmative, it will follow; that the effect of the perception, while it engages the attention completely to itself, is to produce belief; and that the fpeculative disbelief, according to which our conduct in ordinary cafes is regulated, is the result of a recollection of the various circumftances with which the experiment is accompanied. IF, in fuch a cafe as I have now fuppofed, the appearance exhibited to us is of fuch a nature, as to threaten us with any immediate danger, the effect is the fame as if we were to banish from our thoughts the circumftances of the experiment, and to limit our attention folely to what we perceive: for here the belief, which is the firft effect of the perception, alarms our fears, CHAP. and influences our conduct, before reflexion has time to operate. HI. In a very ingenious optical deception, which was lately exhibited in this city, the image of a flower was presented to the fpectator; and when he was about to lay hold of it with his hand, a ftroke was aimed at him by the image of a dagger. If a perfon who has feen this experiment is afked, in his cooler moments, whether or not he believes the dagger which he faw to be real, he will readily anfwer in the negative; and yet the accurate statement of the fact undoubtedly is, that the first and the proper effect of the perception is belief; and that the disbelief he feels, is the effect of subsequent reflexion. THE fpeculative difbelief which we feel with respect to the illufions of imagination, I conceive to be analogous to our fpeculative disbelief of the existence of the object exhibited to the eye in this optical deception; as our belief that the illufions of imagination are real, while that faculty occupies the mind exclusively, is analogous to the belief produced by the optical deception while the attention is limited to our perception, and is withdrawn from the circumftances in which the experiment is made*. THESE obfervations lead me to take notice of a circumftance with refpect to the belief accompanying perception, which it *It may appear to fome readers rather trifling to add, and yet to others the remark may not be altogether fuperfluous, that it is not my intention to infinuate by the foregoing illuftrations, that the relation between perception and imagination has the moft diftant analogy to that between the perception of the object, and the perception of its optical image. appears III. appears to me neceffary to ftate, in order to render Dr. Reid's CHA P. doctrine on that subject that fubject completely fatisfactory. He has fhewn, that certain fenfations are, by a law of our nature, accompanied with an irresistible belief of the existence of certain qualities of external objects. But this law extends no farther than to the prefent exiftence of the quality; that is, to its existence while we feel the correfponding fenfation. Whence is it then, that we afcribe to the quality, an existence independent of our perception? I apprehend we learn to do this by experience alone. We find that we cannot, as in the cafe of imagination, difmifs or recal the perception of an external object. If I open my eyes, I cannot prevent myself from feeing the profpect which is before me. I learn, therefore, to afcribe to the objects of my fenfes, not only an existence at the time I perceive them, but an independent and a permanent existence. IT is a strong confirmation of this doctrine, that in fleep, when (as I flatter myself I shall afterward fhew) the influence of the will over the train of our thoughts is fufpended, and when, of confequence, the time of their continuance in the mind is not regulated by us, we afcribe to the objects of imagination an independent and permanent exiftence, as we do when awake to the objects of perception. The fame thing happens in those kinds of madness, in which a particular idea takes poffeffion of the attention, and occupies it to the exclufion of every thing elfe. Indeed, madness feems in many cafes to arife entirely from a suspension of the influence of the will over the fucceffion of our thoughts; in consequence of which, the objects of imagination U III. CHA P. gination appear to have an existence independent of our volition; and are therefore, agreeably to the foregoing doctrine, mistaken for realities. NUMBERLESS other illuftrations of the fame general fact occur to me; but the following is, I think, one of the most ftriking. I mention it, in preference to the reft, as it appears to me to connect the doctrine in queftion with fome principles which are now universally admitted among philofophers. THE diftinction between the original and the acquired perceptions of fight, is familiarly known to every one who has the flightest acquaintance with the elements of optics. That this sense, prior to experience, conveys to us the notion of extenfion in two dimenfions only, and that it gives us no information concerning the diftances at which objects are placed from the eye, are propofitions which nobody, I prefume, in the present state of science, will be difpofed to controvert. In what manner we are enabled, by a comparison between the perceptions of fight and thofe of touch, to extend the province of the former sense to a variety of qualities originally perceived by the latter fenfe only, optical writers have explained at great length;` but it is not neceffary for my present purpose to enter into any particular details with refpect to their reasonings on the subject. It is fufficient for me to remark, that, according to the received doctrine, the original perceptions of fight become, in confequence of experience, figns of the tangible qualities of external objects, and of the distances at which they are placed from the organ; and that, although the knowledge we obtain, in this manner, of these qualities II |