To express relation in this manner did not require any effort of comparison. The words _arboris_ and _Herculi_ are not general words intended to denote a particular species of relations which the inventors of those expressions meant, in consequence of some sort of comparison, to separate and distinguish from every other sort of relation. The example, indeed, of this contrivance would soon probably be followed, and whoever had occasion to express a similar relation between any other objects would be very apt to do it by making a similar variation on the name of the co-relative object. This, I say, would probably, or rather certainly happen; but it would happen without any intention or foresight in those who first set the example, and who never meant to establish any general rule. The general rule would establish itself insensibly, and by slow degrees, in consequence of that love of analogy and similarity of sound, which is the foundation of by far the greater part of the rules of grammar. To express relation therefore, by a variation in the name of the co-relative object, requiring neither abstraction, nor generalization, nor comparison of any kind, would, at first, be much more natural and easy, than to express it by those general words called prepositions, of which the first invention must have demanded some degree of all those operations. The number of cases is different in different languages. There are five in the Greek, six in the Latin, and there are said to be ten in the Armenian language. It must have naturally happened that there should be a greater or a smaller number of cases, according as in the terminations of nouns substantive the first formers of any language happened to have established a greater or a smaller number of variations, in order to express the different relations they had occasion to take notice of, before the invention of those more general and abstract prepositions which could supply their place.