323. The indicative is primarily the mood of assertion from which it is an easy step to the use in negative and interrogative sentences. It is also used in Greek (as in other languages) to express mere supposition thus we have εἰ in a conditional protasis with all tenses (εἰ ἦν, εἰ ἔστι, εἰ ἔσται), where there need be no implication either for or against the truth of the supposition thus made. Further, the indicative may be used in certain cases in a conditional apodosis, expressing an imaginary consequence. Again, it may be used in final and object clauses referring to the past or to the future. All such uses, in which the indicative does not assert, may be called modal uses.
The tendency of language appears to be to extend the modal uses of the indicative, and consequently to diminish the range of the other moods. It is found possible, and more convenient, to show the modal character of a clause by means of particles, or from the drift of the context, without a distinct verbal form. It will be seen, on comparing the Homeric and Attic usage, that the indicative has encroached in several points upon the other moods.