He walks (for walked) up to him, and knocks (for knocked) him down. This denotes a single action; and is by no means the natural habitual power of the English present. So, in respect to a future, I beat you if you don't leave off, for I will beat you. This use of the present tense is sometimes called the historic use of the present tense. I find it more convenient to call it the representative use; inasmuch as it is used more after the principles of painting than of history; the former of which, necessarily, represents things as present, the latter, more naturally, describes them as past.
The use of the representative present to express simple actions is unequivocally correct. To the expression, however, of complex actions it gives an illogical character,—As I was doing this he enters (for entered). Nevertheless, such a use of the present is a fact in language, and we must take it as it occurs.
[§ 581]. The present tense can be used instead of the future; and that on the principle of representation. Can a future be used for a present? No.
The present tense can be used instead of the aorist; and that on the principle of representation. Can a past tense, or combination, be used for a present?
In respect to the perfect tense there is no doubt. The answer is in the affirmative. For all purposes of syntax a perfect tense, or a combination equivalent to one, is a present tense. Contrast the expression, I come that I may see; with the expression, I came that I might see; i.e., the present construction with the aorist. Then, bring in the perfect construction, I have come. It differs with the aorist, and agrees with the present. I have come that I may see. The reason for this is clear. There is not only a present element in all perfects, but for the purposes of syntax, the present element predominates. Hence expressions like I shall go, need give us no trouble; even though shall be considered as a perfect tense. Suppose the root, sk-ll to mean to be destined (or fated). Provided we consider the effects of the action to be continued up to the time of speaking, we may say I have been destined to go, just as well as we can say I am destined to go.
The use of the aorist as a present (except so far as both the tenses agree in their power of expressing habitual actions) is a more difficult investigation. It bears upon such expressions as I ought to go, &c., and will be taken up in p. [475].
[§ 582]. Certain adverbs, i.e., those of time, require certain tenses. I am then, I was now, I was hereafter, &c., are contradictory expressions. They are not so much bad grammar as impossible nonsense. Nevertheless, we have in Latin such expressions as
"Ut sumus in ponto ter frigore constitit Ister."
Here the connection of the present and perfect ideas explains the apparent contradiction. The present state may be the result of a previous one; so that a preterite element may be involved in a present expression. Ut sumus=since I have been where I am.