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that thatch belongs to the very nature of a house, and that must be a church which is built of stone, and especially if it has a spire upon it. A child whose uncle has been excessive fond, and his schoolmaster very severe, easily believes, that fondness al. ways belongs to uncles, and that severity is essential to masters or instructors. He has seeu also soldiers with red coats, or ministers with long black gowns, and therefore he persuades himself that these garbs are essential to the characters, and that he is not a minister who has not a loug black gown, nor can he be a soldier who is not dressed in red. It would be well if all such mistakes ended with childhood.
It might be also subjoined, that our complex ideas become confused, not only by uniting or blending together: more simple or single ideas than really belong to them, as in the instances just mentioned; but obscurity and confusion sometimes come upon our ideas also, for want of uniting a sufficient number of single ideas to make the complex one: so if I couceive of a leopard only as a spotted beast, this does not distinguish it from a tyger or a lynx, nor from many dogs or horses, which are spott too; and, therefore, a leopard must have some more ideas added to complete and distinguish it.
I grant that it is a large and free acquaintance with the world, a watchful observation and diligent search into the nature of things, that must fully correct this kind of errors: the rules of logic are not sufficient to do it: but yet the rules of logic may instruct us by what means to distinguish one thing from another, and how to search and mark out, as far as may be, the contents and limits of the nature of distinct beings, and thus may give us great assist. ance towards the remedy of these mistakes.
As the definition of names frees us from that confusion which words introduce, so the definition of things will, in some measure, guard us against that confusion which mingled ideas have introduced : for as a definition of the name explains wbat any word means, so a definition of the thing explains what is the nature of that thing.
In order to form a definition of any thing we must put forth these three acts of the mind.
First, conipare the thing to be defined with other things that are most like to itself, and see wherein its essence or nature agrees with them; and this is called the general nature or genus in a definition : so if you would define what wine is, first compare it with other things like itself, as cyder, perry, &c. and you will find it agrees essentially with them in this, that it is a sort of juice.
Secondly, consider the most remarkable and primary attribute, property, or idea wherein this thing differs from those other things that are most like it; and that is its éssential or specific difference: so wine differs from cyder and perry, and all other juices, in that it is pressed from a grape. This may be called its special nature, which distinguishes it from other juices.
Thirdly, join the general and special nature together, (or which is all one), the genus and the difference, and these make up a definition. So the juice of a grape, or juice pressed from grapes, is the definie tion of wine.
So if I would define what winter is, I consider first wherein it agrees with other things which are most like it, (viz.) summer, spring, autumn, and I find they are all seasons of the year; therefore a season of the year is the genus. Then '1 observe wherein lit differs from these, and that is in the shortness of the days; for it is this which does primarily distinguish it from other seasons; therefore this may be called its special nature of its difference. Then by joining these together I make a definition. Winter is that season of the year wherein the days are shortest. 1 confess indeed this is but a ruder definition of it; for to define it, as an accurate astronomer, I must limit the days, hours, and minutes.
After the same manner, if we would explain or de. fine what the picture of a man is, we consider first the genus, or general nature of it, which is a representation; and herein it agrees with mnany other things, as a statue, a shadow, a print, a verbal description of a man, &c. Then we consider wherein it differs from these, and we find it differs from a verbal description, in that it is a representation to the eye, and not to the ear: it differs from a statue, in that it is a representation upon a flat surface, and not in a solid ngure: it differs from a shadow, in that it is an abiding representation and not a fleeting one: it differs from a print or draught, because it . represents the colours by paint as well as the shape of the object by delineation. Now, so many, or rather so few, of these ideas put together, as are just sufficient to distinguish a picture from all other representations, make up its essential difference, or its special nature; and all these are included in its being painted on a plain surface. Then join this to the genus, which is a representation; and thus you have the complete definition of the picture of a man, (viz.) it is the representation of a man in paint upon a surface (or a plane).
Here it must be observed, that when we speak of the genus and difference as composing a definition, it must always be understood that the nearest genus and specific difference are required.
The next general nature, or the nearest genus, must be used in a definition, because it includes all the rest; and if I would define wine, I must say wine is a juice, which is the nearest gemus; and not say, wine is a liquid, which is a remote general nature; or wine is a substance which is yet more remote, for juice includes both substance and liquid. Besides, neither of these two remote general natures would make any distinction between wine and a thousand other substances or other liquids, a remote genus leaves the thing too much undistinguished.
The specific difference is that primary attribute which distinguishes each species from one another, while they stand ranked under the same general nature or genus. Though wine differs from other li. quids in that it is the juice of a certain fruit, yet this is but a general or generic difference, for it does not
distinguish wine from cyder or perry; the specific difference of wipe therefore is its pressure from the grape: as cyder is pressed from apples; and perry
In definitions also we must use the primary attribute that distinguishes the species or special nature, and not attempt to define wine by its particular tastes, or effects, or other properties, which are but secondary or consequential, when its pressure from the grape is the most obvious and primary distinction of it from all other juices. I confess in some cases it is not so easily known which is the primary idea that distinguishes one thing from another; and therefore some would as soon define winter by the coldness of the season, as by the shortness of the days; though the shortness of the days is doubtless the most just, primary, and philosophical difference betwixt thai and the other seasons of the year, since winter days are always shortest, but not always the coldest; I add also, that the shortness of the days is one cause of the coldness, but the cold is no cause of their shortness.
SECT. V.-Rules of the Definition of Things. The special rules of a good definition are these :
Rule 1. A definition must be universal, or as some call it adequate; that is, it must agree to all the particular species or individuals that are included under the same idea; so the juice of a grape agrees to all proper wines, whether red, white, French, Spanish, Florence, &c.
Rule 11. It must be proper and peculiar to the thing defined, and agree to that alone; for it is the very design of a definition effectually to distinguish one thing from all others: so the juice of a grape agrees to no other substance, to no other liquid, to no other being but wine.
These two rules being observed, will always render a definition reciprocal with the thing defined; which is a scholastic way of speaking, to signify that the definition may be used in any sentence in the place
of the thing defined, or they may be mutually af. firmed concerning each other, or substituted in the room of each other. The juice of the grape is wine, or wine is the juice of the grape. And wheresoever the word wine is used, you may put the juice of the grape instead of it, except when you consider wine rather as a word than a thing, or when it is mentioned in such logical rules.
Rule JII. A definition onght to be clear and plain ; for the design of it is to lead us into the knowledge of the thing defined.
Hence it will follow, that the words used in a definition ought not to be doubtful, and equivocal, and obscure, but as plain and easy as the language will afford: and indeed it is a general rule concerning the definition both of pames and things, that no word should be used in either of them, wbich has any darkness or difficulty in it, unless it has been before explained or defined.
Hence it will follow also, that there are many things which cannot well be defined, either as to the name of the thing, unless it be by synonymous words, or by a negation of the contrary idea, &c. for learned men know not how to make them more evident or more intelligible than the ideas which every man has gained by the vulgar methods of teaching. Such are the ideas of extension, duration, thought, consciousness, and most of our simple ideas, and particularly sensible qualities, as white, blue, red, cold, heat, sweet, bitter, sour, &c.
We can say of duration that it is a continuance in being, or a 'not ceasing to be; we can say of consciousness, that it is as it were a feeling within ourselves; we may say, heat is that which is not cold; or sour is that which is like viuegar; or we may point to the clear sky, and say that is blue. These are the vulgar methods of teaching the definitions of names, or meaning of words. But there are some philosophers, whose attempts to define these things learnedly, have wrapt up their ideas in greater darkness, and exposed themselves to ridicule and con