THESE loose hints I have thrown together, in order to excite the curiofity of philofophers, and beget a fufpicion at leaft, if not a full perfuafion, that this fubject is very copious, and that many operations of the human mind depend on the connexion or affociation of ideas, which is here explained. Particularly, the fympathy between the paffions and imagination will, perhaps, appear remarkable; while we obferve that the affections, excited by one object, pafs eafily to another connected with it; but transfuse themselves with difficulty, or not at all, along different objects, which have no manner of connexion together. By introducing, into any compofition, perfonages and actions, foreign to each other, an injudicious author lofes that communication of emotions, by which alone he can intereft the heart, and raise the paffions to their proper height and period. The full explication of this principle and all its confequences would lead us into reafonings too profound and too copious for this enquiry. Tis fufficient, at present, to have eftablished this conclufion, that the three connecting principles of all ideas are the relations of Refemblance, Contiguity, and Caufation.

SECTION IV.

SCEPTICAL DOUBTS CONCERNING THE OPERATIONS OF THE UNDERSTANDING.

A'

PART 1.

LL the objects of human reafon or enquiry may naturally be divided into two kinds, viz. Relations of Ideas and Matters of Fact. Of the firft kind are the Tciences of Geometry, Algebra, and Arithmetic, and in fhort, every affirmation, which is either intuitively or demonftratively certain. That the fquare of the bypotberufe is equal to the fquares of the two fides, is a propofition, which expresses. a relation between thefe figures. That three times five is equal to the half of thirty expreffes a relation between thefe numbers. Propofitions of this kind are difcoverable by the mere operation of thought, without dependance on what is where exiftent in the univerfe. Tho' there never were a true circle or triangle in nature, the truths demonstrated by EUCLID, would for ever retain their certainty and evidence.

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MATTERS of fact, which are the fecond objects of human reafon, are not ascertained in the fame manner; nor is our evidence of their truth, however great, of a like nature with the foregoing. The contrary of every matter of fact is still poffible; because it can never imply a contradiction, and is conceived by the mind with equal facility and diftinctnefs, as if ever fo conformable to reality. That the fan will not rife to-morrow is no lefs intelligible a propofition, and implies no more contradiction, than the affirmation, that it will rife. We fhould in vain, therefore, attempt to demonstrate its falfhood. Were it demonftratively falfe, it

would

would imply a contradiction, and could never be diftinctly conceived by the mind.

IT may, therefore, be a fubject, worthy curiofity, to enquire what is the nature of that evidence, which affures us of any real exiftence and matter of fact, beyond the present teftimony of our fenfes, or the records of our memory. This part of philofophy, 'tis obfervable, has been little cultivated, either by the ancients or moderns; and therefore our doubts and errors, in the profecution of fo important an enquiry, may be the more excufable, while we march thro' fuch difficult paths, without any guide or direction. They may even prove ufeful, by exciting cu riofity, and destroying that implicit faith and fecurity, which is the bane of all reafoning and free enquiry. The difcovery of defects in the common philofophy, if any fuch there be, will not, I prefume, be a difcouragement, but rather an incitement, as is ufual, to attempt fomething more full and fatisfactory, than has yet been propofed to the public.

ALL reafonings concerning matter of fact feem to be founded in the relation of Caufe and Effect. By means of that relation alone can we go beyond the evidence of our memory and fenfes. If you were to afk a man, why he believes any matter of fact, which is abfent; for instance, that his friend is in the country, or in FRANCE; he would give you a reafon; and this reafon would be fome other fact; as a letter received from him, or the knowlege of his former refolutions and promifes. A man, finding a watch or any other machine in a defert island, would conclude, that there had once been men in that island. All our reafonings concerning fact are of the fame nature. And here 'tis conftantly fuppofed, that there is a connexion between the prefent fact and that inferred from it. Were there nothing to bind them together, the inference would be entirely precarious. The hearing of an articulate voice and rational difcourfe in the dark affures us of the prefence of fome perfon: Why? because these are the effects of the human make and fabric, and closely connected with it. If we anatomize all the other reafonings of this nature, we fhall find, that they are founded in the relation of cause and effect, and that this relation is either, near or remote, direct or collateral. Heat and light are collateral effects of fire, and the one effect may justly be inferred from the other.

If we would fatisfy ourselves, therefore, concerning the nature of that evidence, which affures us of all matters of fact, we muft'enquire how we arrive at the knowlege of caufe and effect.

I SHALL venture to affirm, as a general propofition, which admits of no exception, that the knowlege of this relation is not, in any inftance, attained by reafonings à priori; but arifes entirely from experience, when we find, that any particular objects are conftantly conjoined with each other. Let an object be prefented to a man of ever fo ftrong natural reafon and abilities; if that object be entirely new to him, he will not be able, by the most accurate examination of its fenfible qualities, to difcover any of its caufes or effects. ADAM, tho' his rational faculties be fuppofed, at the very firft, entirely perfect, could not have inferred from the fluidity and tranfparency of water, that it would fuffocate him, or from the light and warmth of fire, that it would confume him. No object ever discovers, by the qualities which appear to the fenfes, either the causes, which produced it, or Q ૧ ૩

the

the effects, which will arife from it; nor can our reafon, unaffifted by experience, ever draw any inferences concerning real existence and matter of fact.

THIS propofition, that caufes and effects are difcoverable, not by reason but by experience, will readily be admitted with regard to fuch objects, as we remember to have been once altogether unknown to us; fince we must be conscious of the utter inability which we then lay under of foretelling what would arife from them. Present two fmooth pieces of marble to a man, who has no tincture of natural philofophy; he will never difcover, that they will adhere together, in fuch a manner as to require great force to separate them in a direct line, while they make so small refiftance to a lateral preffure. Such events, as bear little analogy to the common course of nature, are alfo readily confeffed to be known only by experience; nor does any man imagine that the explosion of gunpowder, or the attraction of a loadstone could ever be difcovered by arguments à priori. In like manner, when an effect is fuppofed to depend upon an intricate machinery or fecret structure of parts, we make no difficulty to attribute all our knowlege of it to experience. Who will affert, that he can give the ultimate reason, why milk or bread is proper nourishment for a man, not for a lion or a tyger?

BUT the fame truth may not appear, at firft fight, to have the fame evidence with regard to events, which have become familiar to us from our first appearance in the world, which bear a close analogy to the whole course of nature, and which are fuppofed to depend on the fimple qualities of objects, without any secret ftructure of parts. We are apt to imagine, that we could difcover these effects, by the mere operations of our reafon, without experience. We fancy, that, were we brought, on a fudden, into this world, we could at first have inferred, that one Billiard-ball would communicate motion to another upon impulse; and that we needed not to have waited for the event, in order to pronounce with certainty concerning it. Such is the influence of cuftom, that, where it is ftrongeft, it not only covers our natural ignorance, but even conceals itself, and seems not to take place, merely because it is found in the highest degree.

BUT to convince us, that all the laws of nature and all the operations of bodies, without exception, are known only by experience, the following reflections may, perhaps, fuffice. Were any object prefented to us, and were we required to pronounce concerning the effect, which will refult from it, without confulting past observation; after what manner, I beseech you, muft the mind proceed in this operation? It must invent or imagine fome event, which it afcribes to the object as its effect; and 'tis plain that this invention must be entirely arbitrary. The mind can never poffibly find the effect in the fuppofed caufe, by the most accurate fcrutiny and examination. For the effect is totally different from the caufe, and confequently can never be discovered in it. Motion in the second Billiard-ball is a quite diftinct event from motion in the first; nor is there any thing in the one to fuggeft the smallest hint of the other. A ftone or piece of metal raised into the air, and left without any fupport, immediately falls: But to confider the matter à priori; is there any thing we difcover in this fituation, which can beget the idea of a downward, rather than an upward, or any other motion, in the ftone or metal?

AND as the first imagination or invention of a particular effect, in all natural operations, is arbitrary, where we confult not experience; fo muft we also esteem

the

the fuppofed tye or connexion between the cause and effect, which binds them together, and renders it impoffible, that any other effect could refult from the operation of that caufe. When I fee, for inftance, a Billiard-ball moving in a strait line towards another; even fuppofe motion in the fecond ball fhould by accident be fuggested to me, as the refult of their contact or impulfe; may I not conceive, that a hundred different events might as well follow from that caufe? May not both these balls remain at abfolute reft? May not the first ball return in a ftrait line, or leap off from the fecond in any line or direction? All these fuppofitions are confiftent and conceivable. Why then fhould we give the preference to one, which is no more confiftent nor conceivable than the reft? All our reafonings à priori will never be able to fhew us any foundation for this preference.

In a word, then, every effect is a diftinct event from its caufe. It could not, therefore, be discovered in the cause, and the first invention or conception of it, à priori, must be entirely arbitrary. And even after it is fuggefted, the conjunction of it with the cause must appear equally arbitrary; fince there are always many other effects, which, to reafon, muft feem fully as confiftent and natural. In vain, therefore, fhould we pretend to determine any fingle event, or infer any cause or effect, without the affiftance of obfervation and experience.

HENCE We may discover the reafon, why no philofopher, who is rational and modeft, has ever pretended to affign the ultimate caufe of any natural operation, or to show distinctly the action of that power, which produces any fingle effect in the universe. 'Tis confeffed, that the utmost effort of human reafon is, to reduce the principles, productive of natural phænomena, to a greater fimplicity, and to refolve the many particular effects into a few general caufes, by means of reafonings from analogy, experience, and obfervation. But as to the caufes of thefe general caufes, we fhould in vain attempt their discovery; nor fhall we ever be able to fatisfy ourselves, by any particular explication of them. These ultimate fprings and principles are totally fhut up from human curiofity and enquiry. Elafticity, gravity, cohesion of parts, communication of motion by impulse; these are probably the ultimate causes and principles which we fhall ever discover in nature; and we may esteem ourselves fufficiently happy, if, by accurate enquiry and reasoning, we can trace up the particular phænomena to, or near to, thefe general principles. The moft perfect philofophy of the natural kind only ftaves off our ignorance a little longer: As perhaps the moft perfect philofophy of the moral or metaphyfical kind ferves only to difcover larger portions of our ignorance. Thus the obfervation of human blindness and weakness is the refult of all philofophy, and meets us, at every turn, in fpite of our endeavors to elude, or avoid it. NOR is geometry, when taken into the affiftance of natural philofophy, ever able to remedy this defect, or lead us into the knowlege of ultimate caufes, by all that accuracy of reasoning, for which it is fo juftly celebrated. Every part of mixed mathematics goes upon the fuppofition, that certain laws are established by nature in her operations; and abftract reafonings are employed, either to affist experience in the discovery of these laws, or to determine their influence in particular inftances, where it depends upon any precife degrees of diftance and quantity.. Thus 'tis a law of motion, difcovered by experience, that the moment or force of any body in notion is in the compound ratio or proportion of its folid contents and its velocity; and confequently, that a fmall force may remove the greatest ob

3

ftacle

flacle or raife the greatest weight, if by any contrivance or machinery we can encreafe the velocity of that force, fo as to make it an overmatch for its antagonist. Geometry affifts us in the application of this law, by giving us the juft dimenfions of all the parts and figures, which can enter into any fpecies of machine; but ftill the difcovery of the law itself is owing merely to experience, and all the abftract reafonings in the world could never lead us one step towards the knowlege of it. When we reason à priori, and confider merely any object or caufe, as it ap-. pears to the mind, independent of all obfervation, it never could fuggeft to us the notion of any diftinct object, fuch as its effect; much lefs, fhew us the infeparable and inviolable connection between them. A man must be very fagacious, who could discover by reafoning, that cryftal is the effect of heat and ice of cold, without being previously acquainted with the operations of these qualities.

PART II.

BUT we have not, as yet, attained any tolerable fatisfaction with regard to the queftion firft propofed. Each folution ftill gives rife to a new question as difficult as the foregoing, and leads us on to farther enquiries. When it is asked, What is the nature of all our reafonings concerning matter of fact? The proper anfwer seems to be, that they are founded on the relation of caufe and effect. When again it is afked, What is the foundation of all our reasonings and conclufions concerning that relation? it may be replied in one word, EXPERIENCE. But if we ftill carry on our fifting humor, and afk, What is the foundation of all our conclufions from experience? this implies a new queftion, which may be of more difficult folution and explication. Philofophers, that give themselves airs of fuperior wisdom and fufficiency, have a hard task, when they encounter perfons of inquifitive difpofitions, who push them from every corner, to which they retreat, and who are fure at last to bring them to fome dangerous dilemma. The best expedient to prevent this confufion, is to be modeft in our pretenfions; and even to discover the difficulty ourselves before it is objected to us. By this means, we may make a kind of merit of our very ignorance.

I SHALL Content myself, in this fection, with an eafy tafk, and fhall pretend only to give a negative answer to the queftion here propofed. I fay then, that even after we have experience of the operations of caufe and effect, our conclufions from that experience are not founded on reafoning, or any procefs of the understanding. This answer we must endeavor, both to explain and to defend.

IT muft certainly be allowed, that nature has kept us at a great diftance from all her fecrets, and has afforded us only the knowlege of a few fuperficial qualities of objects, while fhe conceals from us thofe powers and principles, on which the influence of these objects entirely depends. Our fenfes inform us of the color, weight, and confiftence of bread; but neither fenfes nor reafon ever can inform us of thofe qualities, which fit it for the nourishment and support of a human body. Sight or feeling conveys an idea of the actual motion of bodies; but as to that wonderful force or power, which would carry on a moving body for ever in a continued change of place, and which bodies never lofe but by communicating it to others; of this we cannot form the most distant conception. But

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