The Affirmative or Indicative Mood expresses affirmation, and is used in affirmative propositions only, as, Do bhuail mi I struck, bha mi ag bualadh I was striking.
The Negative or Interrogative Mood is used in negative propositions and interrogative clauses, after the Particles ni not, cha not, nach which not, that not, not? mur if not; also, gu, gur, that, an, am, whether used relatively or interrogatively; as, cha d'fholaich mi I did not hide, mur buail sinn if we shall not strike, nach robh iad that they were not, gu robh iad that they were; am buail mi? shall I strike? It is used in the Future Tense after ged although; as, ged bhuail e mi, though he strike me[[57]].
The Subjunctive Mood is used in the Preterite, either with or without conjunctions; as, bhuailinn I would strike, na'm, mur, nach, &c., buailinn if, unless, &c., I should strike. In the Future it is used only after the conjunctions ma if, o, o'n since, and the Relative a expressed or understood; as, ma bhuaileas mi if I shall strike, am fear a bhuaileas mi the man
who will strike me, or the man whom I shall strike; an uair a bhuaileas mi, tra bhuaileas mi the time [in] which I shall strike, i. e., when I shall strike; c'uin [cia ùine] a bhuaileas mi? what [is] the time [in] which I shall strike? i. e., when shall I strike?
The Imperative Mood expresses desire, whether purpose, command, or request; as, buaileam let me strike, buailibh strike ye.
The Infinitive[[58]] is, in all respects, a noun, denoting the action or energy of the verb, and commonly preceded by a Preposition which marks the time of the action; as, ag bualadh at striking, am bualadh the striking, the threshing. It assumes a regular genitive case, bualadh g. s. bualaidh; as, urlar-bualaidh a threshing floor. The Infinitive sometimes loses the termination, and is regularly declined in its abridged form; thus, cruinnich assemble, inf. cruinneach-adh per. apocop. cruinneach g. s. cruinnich; hence, àite-cruinnich a place of meeting, Acts xix. 29, 31, so, fear-criochnaich, Heb. xii. 2, fear-cuidich, Psalm xxx. 10, liv. 4, ionad-foluich, Psalm xxxii. 7, cxix. 114, litir-dhealaich, Matt. v. 31[[59]].
There is no part of the Active Voice that can, strictly speaking, be denominated a Participle. The Infinitive preceded by the Preposition ag at, corresponds in meaning to the present Participle; and preceded by iar after, it corresponds to the participle of the past time; as, ag bualadh at striking, or striking; iar bualadh after striking, or struck[[60]].
Many words, expressing state or action, take the Preposition ag before them, and may be considered as Infinitives of Verbs, whereof the other parts are not in use; as, ag atharrais mimicking, ag gàireachdaich laughing, a' fanoid, a' magadh mocking, jeering.