This amounts to the question: What words significant of definite periods of time were in use, and consequently at the writer's command, at this time? No language is very rich in such words; but in the early Hebrew they seem to have been very scanty. The day, week, month, year, and generation (this last usually implying the time from the birth of a man to that of his son, but possibly in Gen. xv. 16, a century) are all that we find. These in their literal sense were evidently inadequate. Nor could the deficiency be supplied by numerals, even if the general style of the narrative would have admitted their use, for we find in Genesis no numeral beyond the thousand. There was no word at all in early Hebrew equivalent to our words "period" and "season." When such an idea was to be expressed, it was done by the use of the word "day," either in the singular, or more commonly in the plural. Thus, "the time of harvest;" "the season of the first ripe fruit," are literally "the days of harvest," "the days of the first ripe fruit." In Isaiah xxxiv. 8, the singular is used, and followed by the word year in the same indefinite sense. "It is the day of the Lord's vengeance, and the year of recompenses for the controversy of Zion." The only method then which was open to the writer was to make use of one of the words above mentioned in an extended sense, just as he used the word [Hebrew script] (earth) in several senses. But if one of them was to be employed, the one which he has chosen seems the best; not only because its use in that way was common, but because the brevity of the time covered by its natural significance would in itself be a hint of the way in which it was used. That which was impossible in a day might be possible in a year or a generation. The extended significance of the word would become apparent just in proportion as the time covered by its natural significance was inadequate for the processes ascribed to it. An additional reason may, perhaps, be found for the choice of the word "day," in the accordance of its phenomena with some, at least, of the processes which Moses describes--the dawn, the light slowly increasing to the perfect day, and then fading away gradually into night--these do seem aptly to represent the first scanty appearance, the gradual increase, and the vast development of plants, of the reptiles and of the mammalia, and in the case of the first two classes, their gradual passing away.