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Secondly, As we suppose our objects in general to resemble our perceptions, so we take it for granted, that every particular object resembles that perception, which it causes. The relation of cause and effect determines us to join the other of resemblance; and the ideas of these existences being already united together in the fancy by the former relation, we naturally add the latter to compleat the union. We have a strong propensity to compleat every union by joining new relations to those which we have before observed betwixt any ideas, as we shall have occasion to observe presently. [Sect. 5.]
Having thus given an account of all the systems both popular and philosophical, with regard to external existences, I cannot forbear giving vent to a certain sentiment, which arises upon reviewing those systems. I begun this subject with premising, that we ought to have an implicit faith in our senses, and that this would be the conclusion, I should draw from the whole of my reasoning. But to be ingenuous, I feel myself at present of a quite contrary sentiment, and am more inclined to repose no faith at all in my senses, or rather imagination, than to place in it such an implicit confidence. I cannot conceive how such trivial qualities of the fancy, conducted by such false suppositions, can ever lead to any solid and rational system. They are the coherence and constancy of our perceptions, which produce the opinion of their continued existence; though these qualities of perceptions have no perceivable connexion with such an existence. The constancy of our perceptions has the most considerable effect, and yet is attended with the greatest difficulties. It is a gross illusion to suppose, that our resembling perceptions are numerically the same; and it is this illusion, which leads us into the opinion, that these perceptions are uninterrupted, and are still existent, even when they are not present to the senses. This is the case with our popular system. And as to our philosophical one, it is liable to the same difficulties; and is over-and-above loaded with this absurdity, that it at once denies and establishes the vulgar supposition. Philosophers deny our resembling perceptions to be identically the same, and uninterrupted; and yet have so great a propensity to believe them such, that they arbitrarily invent a new set of perceptions, to which they attribute these qualities. I say, a new set of perceptions: For we may well suppose in general, but it is impossible for us distinctly to conceive, objects to be in their nature any thing but exactly the same with perceptions. What then can we look for from this confusion of groundless and extraordinary opinions but error and falshood? And how can we justify to ourselves any belief we repose in them?
This sceptical doubt, both with respect to reason and the senses, is a malady, which can never be radically cured, but must return upon us every moment, however we may chace it away, and sometimes may seem entirely free from it. It is impossible upon any system to defend either our understanding or senses; and we but expose them farther when we endeavour to justify them in that manner. As the sceptical doubt arises naturally from a profound and intense reflection on those subjects, it always encreases, the farther we carry our reflections, whether in opposition or conformity to it. Carelessness and in-attention alone can afford us any remedy. For this reason I rely entirely upon them; and take it for granted, whatever may be the reader's opinion at this present moment, that an hour hence he will be persuaded there is both an external and internal world; and going upon that supposition, I intend to examine some general systems both ancient and modern, which have been proposed of both, before I proceed to a more particular enquiry concerning our impressions. This will not, perhaps, in the end be found foreign to our present purpose.
Several moralists have recommended it as an excellent method of becoming acquainted with our own hearts, and knowing our progress in virtue, to recollect our dreams in a morning, and examine them with the same rigour, that we would our most serious and most deliberate actions. Our character is the same throughout, say they, and appears best where artifice, fear, and policy have no place, and men can neither be hypocrites with themselves nor others. The generosity, or baseness of our temper, our meekness or cruelty, our courage or pusilanimity, influence the fictions of the imagination with the most unbounded liberty, and discover themselves in the most glaring colours. In like manner, I am persuaded, there might be several useful discoveries made from a criticism of the fictions of the antient philosophy, concerning substances, and substantial form, and accidents, and occult qualities; which, however unreasonable and capricious, have a very intimate connexion with the principles of human nature.
It is confest by the most judicious philosophers, that our ideas of bodies are nothing but collections formed by the mind of the ideas of the several distinct sensible qualities, of which objects are composed, and which we find to have a constant union with each other. But however these qualities may in themselves be entirely distinct, it is certain we commonly regard the compound, which they form, as ONE thing, and as continuing the SAME under very considerable alterations. The acknowledged composition is evidently contrary to this supposed simplicity, and the variation to the identity. It may, therefore, be worth while to consider the causes, which make us almost universally fall into such evident contradictions, as well as the means by which we endeavour to conceal them.
It is evident, that as the ideas of the several distinct, successive qualities of objects are united together by a very close relation, the mind, in looking along the succession, must be carryed from one part of it to another by an easy transition, and will no more perceive the change, than if it contemplated the same unchangeable object. This easy transition is the effect, or rather essence of relation; I and as the imagination readily takes one idea for another, where their influence on the mind is similar; hence it proceeds, that any such succession of related qualities is readily considered as one continued object, existing without any variation. The smooth and uninterrupted progress of the thought, being alike in both cases, readily deceives the mind, and makes us ascribe an identity to the changeable succession of connected qualities.
But when we alter our method of considering the succession, and instead of traceing it gradually through the successive points of time, survey at once Any two distinct periods of its duration, and compare the different conditions of the successive qualities; in that case the variations, which were insensible when they arose gradually, do now appear of consequence, and seem entirely to destroy the identity. By this means there arises a kind of contrariety in our method of thinking, from the different points of view, in which we survey the object, and from the nearness or remoteness of those instants of time, which we compare together. When we gradually follow an object in its successive changes, the smooth progress of the thought makes us ascribe an identity to the succession; because it is by a similar act of the mind we consider an unchangeable object. When we compare its situation after a considerable change the progress of the thought is broke; and consequently we are presented with the idea of diversity: In order to reconcile which contradictions the imagination is apt to feign something unknown and invisible, which it supposes to continue the same under all these variations; and this unintelligible something it calls a substance, or original and first matter.
