34. Grammarians have often failed in their definitions, because it is impossible to define certain terms in the way in which the description has been commonly attempted. He who undertakes what is impossible must necessarily fail; and fail too, to the discredit of his ingenuity. It is manifest that whenever a generic name in the singular number is to be defined, the definition must be founded upon some property or properties common to all the particular things included under the term. Thus, if I would define a globe, a wheel, or a pyramid, my description must be taken, not from what is peculiar to one or an other of these things, but from those properties only which are common to all globes, all wheels, or all pyramids. But what property has unity in common with plurality, on which a definition of number may be founded? What common property have the three cases, by which we can clearly define case? What have the three persons in common, which, in a definition of person, could be made evident to a child? Thus all the great classes of grammatical modifications, namely, persons, numbers, genders, cases, moods, and tenses, though they admit of easy, accurate, and obvious definitions in the plural, can scarcely be defined at all in the singular. I do not say, that the terms person, number, gender, case, mood, and tense, ia their technical application to grammar, are all of them equally and absolutely undefinable in the singular; but I say, that no definition, just in sense and suitable for a child, can ever be framed for any one of them. Among the thousand varied attempts of grammarians to explain them so, there are a hundred gross solecisms for every tolerable definition. For this, as I have shown, there is a very simple reason in the nature of the things.