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force and vigour; renders its influence on the paffions and affections more fenfible; and in a word, begets that reliance or fecurity, which conftitutes the nature of belief and opinion.

The cafe is the fame with the probability of caufes as with that of chance: There are fome caufes which are entirely uniform and conftant in producing a particular effect; and no inftance has ever yet been found of any failure or irregularity in their operation. Fire has always burned, and water fuffocated, every human creature: The production of motion by impulfe and gravity is an universal law, which has hitherto admitted of no exception. But there are other causes, which have been found more irregular and uncertain; nor has rhubarb always proved a purge, or opium a foporific, to every one who has taken thefe medicines. It is true, when any cause fails of producing its ufual effect, philofophers afcribe not this to any irregularity in nature; but fuppofe, that fome fecret caufes, in the particular ftructure of parts, have prevented the operation. Our reasonings, however, and conclufions concerning the event, are the fame as if this principle had no place. Being determined by cuftom to transfer the past to the future, in all our inferences; where the past has been entirely regular and uniform we expect the event with the greatest affurance, and leave no room for any contrary fuppofition. But where different effects have been found to follow from causes, which are to appearance exactly fimilar, all these various effects must occur to the mind in transferring the paft to the future, and enter into our confideration, when we determine the probability of the event. Though we give the preference to that which has been found moft ufual, and believe that this effect will exist, we must not overlook the other effects, but muft affign to each of them a particular weight and authority, in proportion as we have found it to be more or less frequent. It is more probable,

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bable, in almoft every country of EUROPE, that there will be froft fometime in JANUARY, than that the weather will continue open throughout that whole month; though this probability varies according to the different climates, and approaches to a certainty in the more northern kingdoms. Here then it seems evident, that, when we transfer the paft to the future, in order to determine the effect, which will refult from any cause, we transfer all the different events, in the fame proportion as they have appeared in the paft, and conceive one to have existed a hundred times, for inftance, another ten times, and another once. As a great number of views do here concur in one event, they fortify and confirm it to the imagination, beget that fentiment which we call belief, and give its object the preference above the contrary event, which is not fupported by an equal number of experiments, and recurs not fo frequently to the thought in transferring the past to the future. Let any one try to account for this operation of the mind upon any of the received fyftems of philofophy, and he will be fenfible of the difficulty. For my part, I fhall think it fufficient, if the prefent hints excite the curiofity of philofophers, and make them fenfible how defective all common theories are in treating of fuch curious and fuch fublime fubjects.

SEC

(69)

SECTION VII.

Of the IDEA of NECESSARY CONNECTION.

TH

PART I.

HE great advantage of the mathematical fciences above the moral confifts in this, that the ideas of the former, being fenfible, are always clear and determinate, the smallest distinction between them is immediately perceptible, and the fame terms are ftill expreffive of the fame ideas, without ambiguity or variation. An oval is never mistaken for a circle, nor an hyperbola for an ellipfis. The ifofceles and fcalenum are distinguished by boundaries more exact than vice and virtue, right and wrong. If any term be defined in geometry, the mind readily, of itself, fubftitutes, on all occafions, the definition for the term defined: Or even when no definition is employed, the object itself may be prefented to the lenfes, and by that means be fteadily and clearly apprehended. But the finer fentiments of the mind, the operations of the understanding, the various agitations of the paffions, though really in themselves diftinct, eafily escape us, when furveyed by reflection; nor is it in our power to recal the original object, as often as we have occafion to contemplate it. Ambiguity, by this means, is gradually introduced into our reafonings: Similar objects are readily taken to be the fame: And the conclufion becomes, at laft very wide of the premises.

One may fafely, however, affirm, that, if we con

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fider

fider these sciences in a proper light, their advantages and difadvantages nearly compenfate each other, and reduce both of them to a ftate of equality. If the mind, with greater facility, retains the ideas of geometry clear and determinate, it must carry on a much longer and more intricate chain of reafoning, and compare ideas much wider of each other, in order to reach the abftrufer truths of that science. And if moral ideas are apt, without extreme care, to fall into obfcurity and confufion, the inferences are always much fhorter in thefe difquifitions, and the intermediate fteps, which lead to the conclufion, much fewer, than in the fciences which treat of quantity and number. In reality, there is fcarcely a propofition in EUCLID fo fimple, as not to confift of more parts, than are to be found in any moral reafoning which runs not into chimera and conceit. Where we trace the principles of the human mind through a few steps, we may be very well fatisfied with our progrefs; confidering how foon nature throws a bar to all our enquiries concerning caufes, and reduces us to an acknowledgment of our ignorance. The chief obftacle, therefore, to our improvement in the moral or metaphyfical fciences, is the obfcurity of the ideas, and ambiguity of the terms. The principal difficulty in the mathematics is the length of inferences and compass of thought, requilite to the forming of any conclufion. And, perhaps, our progrefs in natural philofophy is chiefly retarded by the want of proper experiments and phænomena, which are often difcovered by chance, and cannot always be found, when requifite, even by the most diligent and prudent enquiry. As moral philofophy feems hitherto 'to have received lefs improvement than either geometry or phyfics, we may conclude, that if there be any difference in this refpect among thefe fciences, the difficulties, which obftruct the progrefs of the former, require fuperior care and capacity to be furmounted.

There

There are no ideas, which occur in metaphyfics, more obfcure and uncertain, than thofe of power, force, energy, or neceffary connection; of which it is every moment neceffary for us to treat in all our dif quifitions. We fhall, therefore, endeavour, in this -fection, to fix, if poffible, the precife meaning of these terms, and thereby remove fome part of that obfcurity which is fo much complained of in this fpecies of philofophy.

It seems a propofition, which will not admit of much difpute, that all our ideas are nothing but copies of our impreffions, or, in other words, that it is impoffible for us to think of any thing, which we have not antecedently felt, either by our external or internal fenfes. I have endeavoured* to explain and prove this propofition, and have expreffed my hopes, that, by a proper application of it, men may reach a greater clearness and precision in philofophical reafonings, than what they have hitherto been able to attain. Complex ideas may, perhaps, be well known by definition, which is nothing but an enumeration of thofe parts or fimple ideas that compofe them. But when we have pufhed up definitions to the moft fimple ideas, and find ftill fome ambiguity and obfcurity; what refource are we then poffeffed of? By what invention can we throw light upon these ideas, and render them altogether precife and determinate to our intellectual view? Produce the impreffions or original fentiments from which the ideas are copied. Thefe impreffions are all ftrong and fenfible. They admit not of ambiguity. They are not only placed in a full light themselves, but may throw light on their correspondent ideas, which lie in obfcurity. And by this means we may, perhaps, attain a new microscope or species of optics, by which, in the moral sciences, the most minute and moft fimple ideas may be fo enlarged as to fall readily under our apprehenfion, and be equally E 4

* Section II.

known