DEFINITION, (dejinire, to mark out a boundary), is the process of stating the exact meaning of a word,by means of other words, or an enumeration of the principal attributes of a thing, in order to convey or explain its nature ; thus, a circle is defined to be a figure whose circumference is every where equidistant from its centre. \Volfius defines a real definition to he a distinct notion, explaining the genesis of a thing; that is, the manner wherein the thing is made, or done ; such is that of a circle, whereby it is said to be formed by the motion of a right line round a fixed point ; on which tooting, what was before instanced as a real defi nition of a circle, amounts to no more than a nominal one.
This notion of a real definition is very strict and just ; and afibrds a sufficient distinction between a real and a nominal one. But though it has the advantages of analogy, distinct mss, and convenience, on its side ; yet being only itself a nominal definition, i. e., a definition of the term real defi nition, we must consider it in the light of an idea fixed arbi trarily to that word, and which Woltius always denotes by that word in the conrse of his book.
Of the parts enumerated in a definition, some are common to other things beside the thing defined ; others are peculiar thereto : the first are called the genus, or kind; and the second, the digiTence. Thus, in the thrmer definition of a circle, by a figure whose circumference is everywhere equi distant from its centre ; the word figure is the kind, as being a name common to all other figures as well as to the circle ; the rest the difference, which specifies or distinguishes this figure from every other. And hence arises that rule of F. de Colonia,
for the making of a definition. " Take," says he, " something that is common to the thing defined with other things, and add to it something that is proper, or peculiar to it ; i. e., join the genus and specific difference, and your will have a defi nition." The special rules for a good definition are these : 1. A definition must be universal or adequate, that is, it most agree to all the particular species, or individuals, that are included under the same idea. 2. It must be proper, and pecu liar to the thing defined, and agree to that alone. These two rules being observed, will always renler a definition reci procal with the thing defined, that is, the definition may be used in the place of the thing defined ; or they may be mutually affirmed concerning each other. 3. A definition should be clear and plain ; and, indeed, it is a general rule concerning the definition both of names and things, than no word should he used in either of them which has any difficulty in it, unless it has been before defined. 4. A definition should be short, so that it must have no tautology in it, nor any words superfluous. 5. Neither the thing defined, nor a mere synonymous name, should make any part of the