Time has an analogy with space, arithmetic with geometry. Not only in musical notes, but in the quantity, quality, accent, rhythm of human speech, trivial or serious, there is a law of proportion. As in things of beauty, as in all nature, in the composition as well as in the motion of all things, there is a similarity of relations by which they are held together.
It would be a mistake to suppose that the analogies of language are always uniform: there may be often a choice between several, and sometimes one and sometimes another will prevail. In Greek there are three declensions of nouns; the forms of cases in one of them may intrude upon another.
Similarly verbs in -omega and -mu iota interchange forms of tenses, and the completed paradigm of the verb is often made up of both. The same nouns may be partly declinable and partly indeclinable, and in some of their cases may have fallen out of use. Here are rules with exceptions; they are not however really exceptions, but contain in themselves indications of other rules. Many of these interruptions or variations of analogy occur in pronouns or in the verb of existence of which the forms were too common and therefore too deeply imbedded in language entirely to drop out. The same verbs in the same meaning may sometimes take one case, sometimes another.
The participle may also have the character of an adjective, the adverb either of an adjective or of a preposition. These exceptions are as regular as the rules, but the causes of them are seldom known to us.
