ESSAY XL 459 exactly, that if any of the ideas which go to compose the essence of any particular kind of being be never so little varied by ad- dition, diminution,' or alteration, it destroys that kind, and makes it something else. ' Ancient scholastic writers indeed were almost universally agreed, that all natural beings are thus exactly distributed into distinct species, and that each bath" its own indivisible and un- changeable essence: But in our age we are taught tophilosophize with more caution on this subject ; and that great gmiva Mr. Locke has done much toward teaching us. We use the word species, to signify a rank of beings, in each of which we find a collection of those ideas united, which we call its mature or essence, and which we usually join together under one name, and make that stand for the name of a species ; so we call one set of crea- tures men, another monkeys; some are named beasts and others birds ; this metal is gold, that is silver, and the other is lead, ac- cording to the different ideas which we have joined together to make up each of these species or kinds in our way of thinking and speaking. Now in many things it is evident, that by dropping or dimin- ishing some of those ideas which are usually called essential, and by adding or altering others, there may be a considerable change made in some individual being, and yet we range it still in the sane species, and give it the saine name. We usually suppose four feet and a tail, and a power of barking, to beessential to a dog ; but suppose a dóg had neither a tail, or a tongue, dowe not call it adog still ? Or if the beast should he a little monstrous and should have fivefeet, would it cease to be a dog P But if these ideas which we usually call essential should be very greatly changed, thence there would arise so great a varia- tion from what we call one kind of beings, and such an approxi- mation towards another, that it may sometimes he very hard to know under what kind or species to rank the being in question, and what general name to give it. This is very easy to conceive in things rnoal or artificial (1.) in moral ideas : 'l'he will of a parent may be manifested to a son in such soft and persuasive sort of language, that it is hard to say whether it must be called a counsel or a command. A voluntary action may have so many circumstances in it both good and bad, that it may be a difficulty to determine whether it is virtuous or vicious, lawful or unlawful. (2.) In things artificial ; A hat and acap are different kinds of coverings for the head : A hat has brims all round a cap has not : Yet the brims of the hat may be so lessened by degrees, or cut into such a shape, that you would not know whether to pall it a cap or a hat. The same gradual change may he made in a chair or stool, by lessening or enlarging the hack of it. And so in agarden or orchard, by multiplying or diminishing the num- ber of fruit- trees.
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