2. Whenever the conjunctions if, though, unless, except, whether, lest, or any others, denote contingency or doubt, the verbs that follow them are in the subjunctive mood; as, "If he ride out every day, his health will probably improve;" that is, if he shall or should ride out hereafter. But when these conjunctions do not imply doubt, &c. the verbs that follow them are in the indicative, or some other mood; as, "Though he rides out daily, his health is no better." The conjunctive and indicative forms of this mood, are explained in the conjugation of the verb to love. See page.
The IMPERATIVE MOOD is used for commanding, exhorting, entreating, or permitting; as, "Depart thou; Remember my admonitions; Tarry awhile longer; Go in peace."
The verb depart expresses a command; remember exhorts; tarry expresses entreaty; and go, permission; therefore they are all in the imperative mood.
The imperative, from impero, to command, is literally that mood of the verb used in commanding; but its technical meaning in grammar is extended to the use of the verb in exhorting, entreating, and permitting.
A verb in the imperative mood, is always of the second person, though never varied in its terminations, agreeing with thou, ye, or you, either expressed or implied. You may know a verb in this mood by the sense; recollect, however, that the nominative is always second person, and frequently understood; as, George, give me my hat; that is, give thou, or give you. When the nominative is expressed, it is generally placed after the verb; as, Go thou; Depart ye; or between the auxiliary and the verb; as, Do thou go; Do ye depart. (Do is the auxiliary.)
The POTENTIAL MOOD implies possibility, liberty, or necessity, power, will, or obligation; as, "It may rain; He may go or stay; We must eat and drink; I can ride; He would walk; They should learn."
In the first of these examples, the auxiliary may implies possibility; in the second it implies liberty; that is, he is at liberty to go or to stay; in the third, must denotes necessity; can denotes power or ability; would implies will or inclination; that is, he had a mind to walk; and should implies obligation. Hence you perceive, that the verbs, may rain, may go, must eat, must drink, can ride, world walk, and should learn, are in the potential mood.
NOTE 1. As a verb in the indicative mood is converted into the subjunctive when it is preceded by a conjunction expressing doubt, contingency, supposition, &c., so a verb in the potential mood, may, in like manner, be turned into the subjunctive; as, "If I could deceive him, I should abhor it; Though he should increase in wealth, he would not be charitable." I could deceive, is in the potential; If I could deceive, is in the subjunctive mood.
2. The potential mood, as well as the indicative, is used in asking a question; as, "May I go? Could you understand him? Must we die?"
The INFINITIVE MOOD expresses action, passion, or being, in a general and unlimited manner, having no nominative, consequently, neither person nor number; as, "To speak, to walk."