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_. "_Must_ necessitatem innuit. Debeo, oportet, necesse est urere, _I must burn_. Aliquando sed rarius in præterito dicitur _must_ (quasi ex _must'd_ seu _must't_ contractum). Sic, si de præterito dicatur, _he must_ (seu _must't_) _be burnt_, oportebat uri seu necesse habuit ut ureretur."--WALLIS, 107. 9. Auxiliary derived from the idea of action--_do_. C. _Classification of auxiliary verbs in respect to their mode of construction._--Auxiliary verbs combine with others in three ways. 1. _With participles._--a) With the present, or active, participle--_I am speaking_: b) With the past, or passive, participle--_I am beaten_, _I have beaten_. 2. _With infinitives._--a) With the objective infinitive--_I can speak_: b) With the gerundial infinitive--_I have to speak_. 3. _With both infinitives and participles._--_I shall have done_, _I mean to have done_. D. _Auxiliary verbs may be classified according to their effect._--Thus--_have_ makes the combination in which it appears equivalent to a tense; _be_ to a passive form; _may_ to a sign of mood, &c. This sketch of the different lights under which auxiliary verbs may be viewed, has been written for the sake of illustrating, rather than exhausting, the subject. § 492. The combination of the auxiliary, _have_, with the past participle requires notice. It is, here, advisable to make the following classifications. 1. The combination with the participle of a _transitive verb._--_I have ridden the horse_; _thou hast broken the sword_; _he has smitten the enemy_. 2. The combination with the participle of an _intransitive_ verb,--_I have waited_; _thou hast hungered_; _he has slept_. 3. The combination with the participle of the verb substantive, _I have been_; _thou hast been_; _he has been_.