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SECTION I: Principles of Reason. - Henry Home, Lord Kames, Sketches of the History of Man, vol. 3 
Sketches of the History of Man Considerably enlarged by the last additions and corrections of the author, edited and with an Introduction by James A. Harris (Indianapolis: Liberty Fund, 2007). 3 Vols. Vol. 3.
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Principles of Reason.
Affirmation is that sort of expression which the speaker uses, when he desires to be believed. What he affirms is termed a proposition.
Truth and error are qualities of propositions. A proposition that says a thing is what it is in reality, is termed a true proposition. A proposition that says a thing is what it is not in reality, is termed an erroneous proposition.
Truth is so essential in conducting affairs, that man would be a disjointed being were it not agreeable to him. Truth accordingly is agreeable to every human being, and falsehood or error disagreeable. The pursuit of truth is no less pleasant than the pursuit of any other good.*1
Our knowledge of what is agreeable and disagreeable in objects is derived from the sense of beauty, handled in Elements of Criticism. Our knowledge of right and wrong in actions, is derived from the moral sense, to be handled in the sketch immediately following. Our knowledge of truth and error is derived from various sources.
Our external senses are one source of knowledge: they lay open to us external subjects, their qualities, their actions, with events produced by these actions. The internal senses are another source of knowledge: they lay open to us things passing in the mind; thinking, for example, deliberating, inclining, resolving, willing, consenting, and other acts; and they also lay open to us our emotions and passions. There is a sense by which we perceive the truth of many propositions; such as, That every thing which begins to exist must have a cause; That every effect adapted to some end or purpose, proceeds from a designing cause; and, That every effect adapted to a good end or purpose, proceeds from a designing and benevolent cause. A multitude of axioms in every science, particularly in mathematics, are equally perceived to be true. By a peculiar sense, of which afterward, we know that there is a Deity. There is a sense by which we know, that the external signs of passion are the same in all men; that animals of the same external appearance, are of the same species, and that animals of the same species, have the same properties(a) . There is a sense that dives into futurity: we know that the sun will rise to-morrow; that the earth will perform its wonted course round the sun; that winter and summer will follow each other in succession; that a stone dropt from the hand will fall to the ground; and a thousand other such propositions.
There are many propositions, the truth of which is not so apparent: a process of reasoning is necessary, of which afterward.
Human testimony is another source of knowledge. So framed we are by nature, as to rely on human testimony; by which we are informed of beings, attributes, and events, that never came under any of our senses.
The knowledge that is derived from the sources mentioned, is of different kinds. In some cases, our knowledge includes absolute certainty, and produces the highest degree of conviction: in other cases, probability comes in place of certainty, and the conviction is inferior in degree. Knowledge of the latter kind is distinguished into belief, which concerns facts; and opinion, which concerns relations, and other things that fall not under the denomination of facts. In contradistinction to opinion and belief, that sort of knowledge which includes absolute certainty, and produces the highest degree of conviction, retains its proper name. To explain what is here said, I enter into particulars.
The sense of seeing, with very few exceptions, affords knowledge properly so termed: it is not in our power to doubt of the existence of a person we see, touch, and converse with. When such is our constitution, it is a vain attempt to call in question the authority of our sense of seeing, as some writers pretend to do. No one ever called in question the existence of internal actions and passions, laid open to us by internal sense; and there is as little ground for doubting of what we see. The sense of seeing, it is true, is not always correct: through different mediums the same object is seen differently: to a jaundic’d eye every thing appears yellow; and to one intoxicated with liquor, two candles sometimes appear four. But we are never left without a remedy in such a case: it is the province of the reasoning faculty to correct every error of that kind.
An object of sight recalled to mind by the power of memory, is termed an idea or secondary perception. An original perception, as said above, affords knowledge in its proper sense; but a secondary perception affords belief only. And Nature in this, as in all other instances, is faithful to truth; for it is evident, that we cannot be so certain of the existence of an object in its absence, as when present.
With respect to many abstract propositions, of which instances are above given, we have an absolute certainty and conviction of their truth, derived to us from various senses. We can, for example, entertain as little doubt that every thing which begins to exist must have a cause, as that the sun is in the firmament; and as little doubt that he will rise to-morrow, as that he is now set. There are many other propositions, the truth of which is probable only, not absolutely certain; as, for example, that winter will be cold and summer warm. That natural operations are performed in the simplest manner, is an axiom of natural philosophy: it may be probable, but is far from being certain.*
In every one of the instances given, conviction arises from a single act of perception: for which reason, knowledge acquired by means of that perception, not only knowledge in its proper sense but also opinion and belief, are termed intuitive knowledge. But there are many things, the knowledge of which is not obtained with so much facility. Propositions for the most part require a process or operation in the mind, termed reasoning; leading, by certain intermediate steps, to the proposition that is to be demonstrated or made evident; which, in opposition to intuitive knowledge, is termed discursive knowledge. This process or operation must be explained, in order to understand the nature of reasoning. And as reasoning is mostly employ’d in discovering relations, I shall draw my examples from them. Every proposition concerning relations, is an affirmation of a certain relation between two subjects. If the relation affirmed appear not intuitively, we must search for a third subject, intuitively connected with each of the others by the relation affirmed: and if such a subject be found, the proposition is demonstrated; for it is intuitively certain, that two subjects connected with a third by any particular relation, must be connected together by the same relation. The longest chain of reasoning may be linked together in this manner. Running over such a chain, every one of the subjects must appear intuitively to be connected with that immediately preceding, and with that immediately subsequent, by the relation affirmed in the proposition; and from the whole united, the proposition, as above mentioned, must appear intuitively certain. The last step of the process is termed a conclusion, being the last or concluding perception.
No other reasoning affords so clear a notion of the foregoing process, as that which is mathematical. Equality is the only mathematical relation; and comparison therefore is the only means by which mathematical propositions are ascertained. To that science belong a number of intuitive propositions, termed axioms, which are all founded on equality. For example: Divide two equal lines, each of them, into a thousand equal parts, a single part of the one line must be equal to a single part of the other. Second: Take ten of these parts from the one line, and as many from the other, and the remaining parts must be equal; which is more shortly expressed thus: From two equal lines take equal parts, and the remainders will be equal; or add equal parts, and the sums will be equal. Third: If two things be, in the same respect, equal to a third, the one is equal to the other in the same respect. I proceed to show the use of these axioms. Two things may be equal without being intuitively so; which is the case of the equality between the three angles of a triangle and two right angles. To demonstrate that truth, it is necessary to search for some other angles that intuitively are equal to both. If this property cannot be discovered in any one set of angles, we must go more leisurely to work, and try to find angles that are equal to the three angles of a triangle. These being discovered, we next try to find other angles equal to the angles now disco-vered; and so on in the comparison, till at last we discover a set of angles, equal not only to those thus introduced, but also to two right angles. We thus connect the two parts of the original proposition, by a number of intermediate equalities; and by that means perceive, that these two parts are equal among themselves; it being an intuitive proposition, as mentioned above, That two things are equal, each of which, in the same respect, is equal to a third.
I proceed to a different example, which concerns the relation between cause and effect. The proposition to be demonstrated is, “That there exists a good and intelligent Being, who is the cause of all the wise and benevolent effects that are produced in the government of this world.” That there are such effects, is in the present example the fundamental proposition; which is taken for granted, because it is verified by experience. In order to discover the cause of these effects, I begin with an intuitive proposition mentioned above, “That every effect adapted to a good end or purpose, proceeds from a designing and benevolent cause.” The next step is, to examine whether man can be the cause: he is provided indeed with some share of wisdom and benevolence; but the effects mentioned are far above his power, and no less above his wisdom. Neither can this earth be the cause, nor the sun, the moon, the stars; for, far from being wise and benevolent, they are not even sensible. If these be excluded, we are unavoidably led to an invisible being, endowed with boundless power, goodness, and intelligence; and that invisible being is termed God.
Reasoning requires two mental powers, namely, the power of invention, and the power of perceiving relations. By the former are discovered intermediate propositions, equally related to the fundamental proposition and to the conclusion: by the latter we perceive, that the different links which compose the chain of reasoning, are all connected together by the same relation.
We can reason about matters of opinion and belief, as well as about matters of knowledge properly so termed. Hence reasoning is distinguished into two kinds; demonstrative, and probable. Demon-strative reasoning is also of two kinds: in the first, the conclusion is drawn from the nature and inherent properties of the subject: in the other, the conclusion is drawn from some principle, of which we are certain by intuition. With respect to the first, we have no such knowledge of the nature or inherent properties of any being, material or immaterial, as to draw conclusions from it with certainty. I except not even figure considered as a quality of matter, tho’ it is the object of mathematical reasoning. As we have no standard for determining with precision the figure of any portion of matter, we cannot with precision reason upon it: what appears to us a straight line may be a curve, and what appears a rectilinear angle may be curvilinear. How then comes mathematical reasoning to be demonstrative? This question may appear at first sight puzzling; and I know not that it has any where been distinctly explained. Perhaps what follows may be satisfactory.
The subjects of arithmetical reasoning are numbers. The subjects of mathematical reasoning are figures. But what figures? Not such as I see; but such as I form an idea of, abstracting from every imperfection. I explain myself. There is a power in man to form images of things that never existed; a golden mountain, for example, or a river running upward. This power operates upon figures: there is perhaps no figure existing the sides of which are straight lines; but it is easy to form an idea of a line that has no waving or crookedness, and it is easy to form an idea of a figure bounded by such lines. Such ideal figures are the subjects of mathematical reasoning; and these being perfectly clear and distinct, are proper subjects for demonstrative reasoning of the first kind. Mathematical reasoning however is not merely a mental entertainment: it is of real use in life, by directing us to operate upon matter. There possibly may not be found any where a perfect globe, to answer the idea we form of that figure: but a globe may be made so near perfection, as to have nearly the properties of a perfect globe. In a word, tho’ ideas are, properly speaking, the subject of mathematical evidence; yet the end and purpose of that evidence is, to direct us with respect to figures as they really exist; and the nearer any real figure approaches to its ideal perfection, with the greater accuracy will the mathematical truth be applicable.
The component parts of figures, viz. lines and angles, are extremely simple, requiring no definition. Place before a child a crooked line, and one that has no appearance of being crooked: call the former a crooked line, the latter a straight line; and the child will use these terms familiarly, without hazard of a mistake. Draw a perpendicular upon paper: let the child advert, that the upward line leans neither to the right nor the left, and for that reason is termed a perpendicular: the child will apply that term familiarly to a tree, to the wall of a house, or to any other perpendicular. In the same manner, place before the child two lines diverging from each other, and two that have no appearance of diverging: call the latter parallel lines, and the child will have no difficulty of applying the same term to the sides of a door or of a window. Yet so accustomed are we to definitions, that even these simple ideas are not suffered to escape. A straight line, for example, is defined to be the shortest that can be drawn between two given points. Is it so, that even a man, not to talk of a child, can have no idea of a straight line till he be told that the shortest line between two points is a straight line? How many talk familiarly of a straight line who never happened to think of that fact, which is an inference only, not a definition. If I had not beforehand an idea of a straight line, I should never be able to find out, that it is the shortest that can be drawn between two points. D’Alembert strains hard, but without success, for a definition of a straight line, and of the others mentioned. It is difficult to avoid smiling at his definition of parallel lines. Draw, says he, a straight line: erect upon it two perpendiculars of the same length: upon their two extremities draw another straight line; and that line is said to be parallel to the first mentioned; as if, to understand what is meant by the expression two parallel lines, we must first understand what is meant by a straight line, by a perpendicular, and by two lines equal in length. A very slight reflection upon the operations of his own mind, would have taught this author, that he could form the idea of parallel lines without running through so many intermediate steps: sight alone is sufficient to explain the term to a boy, and even to a girl. At any rate, where is the necessity of introducing the line last mentioned? If the idea of parallels cannot be obtained from the two perpendiculars alone, the additional line drawn through their extremities will certainly not make it more clear.
Mathematical figures being in their nature complex, are capable of being defined; and from the foregoing simple ideas, it is easy to define every one of them. For example, a circle is a figure having a point within it, named the centre, through which all the straight lines that can be drawn, and extended to the circumference, are equal; a surface bounded by four equal straight lines, and having four right angles, is termed a square; and a cube is a solid, of which all the six surfaces are squares.
In the investigation of mathematical truths, we assist the imagination, by drawing figures upon paper that resemble our ideas. There is no necessity for a perfect resemblance: a black spot, which in reality is a small round surface, serves to represent a mathematical point; and a black line, which in reality is a long narrow surface, serves to represent a mathematical line. When we reason about the figures composed of such lines, it is sufficient that these figures have some appearance of regularity: less or more is of no importance; because our reasoning is not founded upon them, but upon our ideas. Thus, to demonstrate that the three angles of a triangle are equal to two right angles, a triangle is drawn upon paper, in order to keep the mind steady to its object. After tracing the steps that lead to the conclusion, we are satisfied that the proposition is true; being conscious that the reasoning is built upon the ideal figure, not upon that which is drawn upon the paper. And being also conscious, that the enquiry is carried on independent of any particular length of the sides; we are satisfied of the universality of the proposition, and of its being applicable to all triangles whatever.
Numbers considered by themselves, abstractedly from things, make the subject of arithmetic. And with respect both to mathematical and arithmetical reasonings, which frequently consist of many steps, the process is shortened by the invention of signs, which, by a single dash of the pen, express clearly what would require many words. By that means, a very long chain of reasoning is expressed by a few symbols; a method that contributes greatly to readiness of comprehension. If in such reasonings words were necessary, the mind, embarrassed with their multitude, would have great difficulty to follow any long chain of reasoning. A line drawn upon paper represents an ideal line, and a few simple characters represent the abstract ideas of number.
Arithmetical reasoning, like mathematical, depends entirely upon the relation of equality, which can be ascertained with the greatest certainty among many ideas. Hence, reasonings upon such ideas afford the highest degree of conviction. I do not say, however, that this is always the case; for a man who is conscious of his own fallibility, is seldom without some degree of diffidence, where the reasoning consists of many steps. And tho’ on a re-view no error be discovered, yet he is conscious that there may be errors, tho’ they have escaped him.
As to the other kind of demonstrative reasoning, founded on propositions of which we are intuitively certain; I justly call it demonstrative, because it affords the same conviction that arises from mathematical reasoning. In both, the means of conviction are the same, viz. a clear perception of the relation between two ideas: and there are many relations of which we have ideas no less clear than of equality; witness substance and quality, the whole and its parts, cause and effect, and many others. From the intuitive proposition, for example, That nothing which begins to exist can exist without a cause, I can conclude, that some one being must have existed from all eternity, with no less certainty, than that the three angles of a triangle are equal to two right angles.
What falls next in order, is that inferior sort of knowledge which is termed opinion; and which, like knowledge properly so termed, is founded in some instances upon intuition, and in some upon reasoning. But it differs from knowledge properly so termed in the following particular, that it produces different degrees of conviction, sometimes approaching to certainty, sometimes sinking toward the verge of improbability. The constancy and uniformity of natural operations, is a fit subject for illustrating that difference. The future successive changes of day and night, of winter and summer, and of other successions which have hitherto been constant and uniform, fall under intuitive knowledge, because of these we have the highest conviction. As the conviction is inferior of successions that hitherto have varied in any degree, these fall under intuitive opinion. We expect summer after winter with the utmost confidence; but we have not the same confidence in expecting a hot summer or a cold winter. And yet the probability approaches much nearer to certainty, than the intuitive opinion we have, that the operations of nature are extremely simple, a proposition that is little rely’d on.
As to opinion founded on reasoning, it is obvious, that the conviction produced by reasoning, can never rise above what is produced by the intuitive proposition upon which the reasoning is founded. And that it may be weaker, will appear from considering, that even where the fundamental proposition is certain, it may lead to the conclusive opinion by intermediate propositions, that are probable only, not certain. In a word, it holds in general with respect to every sort of reasoning, that the conclusive proposition can never rise higher in point of conviction, than the very lowest of the intuitive propositions employ’d as steps in the reasoning.
The perception we have of the contingency of future events, opens a wide field to our reasoning about probabilities. That perception involves more or less doubt according to its subject. In some instances, the event is perceived to be extremely doubtful; in others, it is perceived to be less doubtful. It appears altogether doubtful, in throwing a dye, which of the six sides will turn up; and for that reason, we cannot justly conclude for one rather than for another. If one only of the six sides be marked with a figure, we conclude, that a blank will turn up; and five to one is an equal wager that such will be the effect. In judging of the future behaviour of a man who has hitherto been governed by interest, we may conclude with a probability approaching to certainty, that interest will continue to prevail.
Belief comes last in order, which, as defined above, is knowledge of the truth of facts that falls below certainty, and involves in its nature some degree of doubt. It is also of two kinds; one founded upon intuition, and one upon reasoning. Thus, knowledge, opinion, belief, are all of them equally distinguishable into intuitive and discursive. Of intuitive belief, I discover three different sources or causes. First, A present object. Second, An object formerly present. Third, The testimony of others.
To have a clear conception of the first cause, it must be observed, that among the simple perceptions that compose the complex perception of a present object, a perception of real and present existence is one. This perception rises commonly to certainty; in which case it is a branch of knowledge properly so termed; and is handled as such above. But this perception falls below certainty in some instances; as where an object, seen at a great distance or in a fog, is perceived to be a horse, but so indistinctly as to make it a probability only. The perception in such a case is termed belief. Both perceptions are fundamentally of the same nature; being simple perceptions of real existence. They differ only in point of distinctness: the perception of reality that makes a branch of knowledge, is so clear and distinct as to exclude all doubt or hesitation: the perception of reality that occasions belief, being less clear and distinct, makes not the existence of the object certain to us, but only probable.
With respect to the second cause; the existence of an absent object, formerly seen, amounts not to a certainty; and therefore is the subject of belief only, not of knowledge. Things are in a continual flux from production to dissolution; and our senses are accommodated to that variable scene: a present object admits no doubt of its existence; but after it is removed, its existence becomes less certain, and in time sinks down to a slight degree of probability.
Human testimony, the third cause, produces belief, more or less strong, accor-ding to circumstances. In general, nature leads us to rely upon the veracity of each other; and commonly the degree of reliance is proportioned to the degree of veracity. Sometimes belief approaches to certainty, as when it is founded on the evidence of persons above exception as to veracity. Sometimes it sinks to the lowest degree of probability, as when a fact is told by one who has no great reputation for truth. The nature of the fact, common or uncommon, has likewise an influence: an ordinary incident gains credit upon very slight evidence; but it requires the strongest evidence to overcome the improbability of an event that deviates from the ordinary course of nature. At the same time, it must be observed, that belief is not always founded upon rational principles. There are biasses and weaknesses in human nature that sometimes disturb the operation, and produce belief without sufficient or proper evidence: we are disposed to believe on very slight evidence, an interesting event, however rare or singular, that alarms and agitates the mind; because the mind in agitation is remarkably susceptible of impressions: for which reason, stories of ghosts and apparitions pass current with the vulgar. Eloquence also has great power over the mind; and, by making deep impressions, enforces the belief of facts upon evidence that would not be regarded in a cool moment.
The dependence that our perception of real existence, and consequently belief, hath upon oral evidence, enlivens social intercourse, and promotes society. But the perception of real existence has a still more extensive influence; for from that perception is derived a great part of the entertainment we find in history, and in historical fables(a) . At the same time, a perception that may be raised by fiction as well as by truth, would often mislead were we abandoned to its impulse: but the God of nature hath provided a remedy for that evil, by erecting within the mind a tribunal, to which there lies an appeal from the rash impressions of sense. When the delusion of eloquence or of dread subsides, the perplexed mind is uncertain what to believe. A regular process commences, counsel is heard, evidence pro-duced, and a final judgement pronounced, sometimes confirming, sometimes varying, the belief impressed upon us by the lively perception of reality. Thus, by a wise appointment of nature, intuitive belief is subjected to rational discussion: when confirmed by reason, it turns more vigorous and authoritative: when contradicted by reason, it disappears among sensible people. In some instances, it is too headstrong for reason; as in the case of hobgoblins and apparitions, which pass current among the vulgar in spite of reason.
We proceed to the other kind of belief, that which is founded on reasoning; to which, when intuition fails us, we must have recourse for ascertaining certain facts. Thus, from known effects, we infer the existence of unknown causes. That an effect must have a cause, is an intuitive proposition; but to ascertain what particular thing is the cause, requires commonly a process of reasoning. This is one of the means by which the Deity, the primary cause, is made known to us, as mentioned above. Reason, in tracing causes from known effects, produces different degrees of conviction. It sometimes produces certainty, as in proving the existence of the Deity; which on that account is handled above, under the head of knowledge. For the most part it produces belief only, which, according to the strength of the reasoning, sometimes approaches to certainty, sometimes is so weak as barely to turn the scale on the side of probability. Take the following examples of different degrees of belief founded on probable reasoning. When Inigo Jones flourished, and was the only architect of note in England; let it be supposed, that his model of the palace of Whitehall had been presented to a stranger, without mentioning the author. The stranger, in the first place, would be intuitively certain, that this was the work of some Being, intelligent and skilful. Secondly, He would have a conviction approaching to certainty, that the operator was a man. And, thirdly, He would have a conviction that the man was Inigo Jones; but less firm than the former. Let us next suppose another English architect little inferior in reputation to Jones: the stranger would still pronounce in favour of the latter; but his belief would be in the lowest degree.
When we investigate the causes of certain effects, the reasoning is often founded upon the known nature of man. In the high country, for example, between Edinburgh and Glasgow, the people lay their coals at the end of their houses, without any fence to secure them from theft: whence it is rationally inferred, that coals are there in plenty. In the west of Scotland, the corn-stacks are covered with great care and nicety: whence it is inferred, that the climate is rainy. Placentia is the capital town of Biscay: the only town in Newfoundland bears the same name; from which circumstance it is conjectured, that the Biscayners were the first Europeans who made a settlement in that island.
Analogical reasoning, founded upon the uniformity of nature, is frequently employ’d in the investigation of facts; and we infer, that facts of which we are uncertain, must resemble those of the same kind that are known. The reasonings in natural philosophy are mostly of that kind. Take the following examples. We learn from experience, that proceeding from the humblest vegetable to man, there are num-berless classes of beings rising one above another by differences scarce perceptible, and leaving no where a single gap or interval: and from conviction of the uniformity of nature we infer, that the line is not broken off here, but is carried on in other worlds, till it end in the Deity. I proceed to another example. Every man is conscious of a self-motive power in himself; and from the uniformity of nature, we infer the same power in every one of our own species. The argument here from analogy carries great weight, because we entertain no doubt of the uniformity of nature with respect to beings of our own kind. We apply the same argument to other animals; tho’ their resemblance to man appears not so certain, as that of one man to another. But why not also apply the same argument to infer a self-motive power in matter? When we see matter in motion without an external mover, we naturally infer, that, like us, it moves itself. Another example is borrow’d from Maupertuis. “As there is no known space of the earth covered with water so large as the Terra Australis incognita, we may reasonably infer, that so great a part of the earth is not altogether sea, but that there must be some proportion of land.” The uniformity of nature with respect to the intermixture of sea and land, is an argument that affords but a very slender degree of conviction; and from late voyages it is discovered, that the argument holds not in fact. The following argument of the same kind, tho’ it cannot be much rely’d on, seems however better founded. “The inhabitants of the northern hemisphere, have, in arts and sciences, excelled such of the southern as we have any knowledge of: and therefore among the latter we ought not to expect many arts, nor much cultivation.”
After a fatiguing investigation of numberless particulars which divide and scatter the thought, it may not be unpleasant to bring all under one view by a succinct recapitulation.
We have two means for discovering truth and acquiring knowledge, viz. intuition and reasoning. By intuition we discover subjects and their attributes, passions, internal action, and in short every thing that is matter of fact. By intuition we also discover several relations. There are some facts and many relations, that cannot be discovered by a single act of intuition, but require several such acts linked together in a chain of reasoning.
Knowledge acquired by intuition, includes for the most part certainty: in some instances it includes probability only. Knowledge acquired by reasoning, frequently includes certainty; but more frequently includes probability only.
Probable knowledge, whether founded on intuition or on reasoning, is termed opinion when it concerns relations; and is termed belief when it concerns facts. Where knowledge includes certainty, it retains its proper name.
Reasoning that produces certainty, is termed demonstrative; and is termed probable, when it only produces probability.
Demonstrative reasoning is of two kinds. The first is, where the conclusion is derived from the nature and inherent properties of the subject: mathematical reasoning is of that kind; and perhaps the only instance. The second is, where the conclusion is derived from some proposition, of which we are certain by intuition.
Probable reasoning is endless in its varieties; and affords different degrees of conviction, depending on the nature of the subject upon which it is employ’d.
[* ]It has been wisely observed, that truth is the same to the understanding that music is to the ear, or beauty to the eye.
[1. ]This paragraph (with note) added in 2nd edition.
[(a) ]Preliminary Discourse.
[* ]I have given this proposition a place, because it is assumed as an axiom by all writers on natural philosophy. And yet there appears some room for doubting, whether our conviction of it do not proceed from a bias in our nature, rather than from an original sense. Our taste for simplicity, which undoubtedly is natural, renders simple operations more agreeable than what are complex, and consequently makes them appear more natural. It deserves a most serious discussion, whether the operations of nature be always carried on with the greatest simplicity, or whether we be not misled by our taste for simplicity to be of that opinion.
[(a) ]Elements of Criticism, ch. 2. part 1. § 7.