“If he say so, it is well,” i.e. “if he shall say so.”
“Though he slay me, yet will I trust in him,” (Bible) i.e. “though he should slay.”
“Though thou detain me, I will not eat,” (Ibid.) i.e. “shouldst detain me.”
“If thy brother trespass against thee,” (Ibid.) i.e. “should trespass.”
“Though he fall, he shall not utterly be cast down,” (Ibid.) i.e. “though he should fall.”
“Remember that thou keep holy the sabbath day,” (Ibid.) i.e. “thou shouldst keep.”
There are a few examples in the use of the auxiliaries do and have, in which, when the ellipsis is supplied, the expression appears somewhat uncouth; but I am persuaded that a little attention will show, that these examples form no exception to this theory.
“If now thou do prosper my way.”—Bible. It is here obvious, that the event supposed was future; the appropriate term, therefore, to express that idea, is either shall or will. If the phrase were, “if thou prosper my way,” it would be universally admitted that the auxiliary is suppressed, thus, “if thou shalt or wilt prosper my way.” Again, when we say, “if thou do it, I shall be displeased,” it is equally evident that the auxiliary is understood, thus, “if thou shalt do it.” Now, if these examples be duly considered, and if the import of the verb to do, as formerly explained, be remembered, I think it will appear that the expression is elliptical, and truly proceeds thus, “if thou (shalt) do prosper my way.” The same observations are applicable to Shakspeare’s phraseology, when he says, “if thou do pardon, whosoever pray.” Again; when Hamlet says, “if damned custom have not brazed it so,” it is obvious that the auxiliary verb may is understood; for, if the expression be cleared of the negative, the insertion of the auxiliary creates no uncouthness; thus, “if damned custom may have brazed it so.”
I am therefore inclined to think, that the conditional form, unless in the verb to be[68], has no existence in our language.