non-auxiliary significations.—The power of the word have in the combination of I have a horse is clear enough. It means possession. The power of the same word in the combination I have been is not so clear; nevertheless it is a power which has grown out of the idea of possession. This shows that the power of a verb as an auxiliary may be a modification of its original power; i.e., of the power it has in non-auxiliary constructions. Sometimes the difference is very little: the word let, in let us go, has its natural sense of permission unimpaired. Sometimes it is lost altogether. Can and may exist only as auxiliaries.
1. Auxiliary derived from the idea of possession—have.
2. Auxiliaries derived from the idea of existence—be, is, was.
3. Auxiliary derived from the idea of future destination, dependent upon circumstances external to the agent—shall. There are etymological reasons for believing that shall is no present tense, but a perfect.
4. Auxiliary derived from the idea of future destination, dependent upon the volition of the agent—will. Shall is simply predictive; will is predictive and promissive as well.
5. Auxiliary derived from the idea of power, dependent upon circumstances external to the agent—may.
6. Auxiliary derived from the idea of power, dependent upon circumstances internal to the agent—can. May is simply permissive; can is potential. In respect to the idea of power residing in the agent being the cause which determines a contingent action, can is in the same relation to may as will is to shall.
"May et can, cum eorum præteritis imperfectis, might et could, potentiam innuunt: cum hoc tamen discrimine: may et might vel de jure vel saltem de rei possibilitate, dicuntur, at can et could de viribus agentis."—Wallis, p. 107.
7. Auxiliary derived from the idea of sufferance—let.
8. Auxiliary derived from the idea of necessity—must.