We have no met the two verbs, atá and bí. We have a third verb which is also used to translate into Irish the English "am, art, is, are", etc.
This verb is is, pronounced (is) like iss in English hiss, not like is in his. This pronunciation is not according to the general rule that s after i should be pronounced (sh).
The English sentences we have met up to this have been like "the day is long", "I am a strong man", "Patrick was a priest" "The house will be on the hill", ec. But in no case have we met a sentence where the English verb am, art, is, are, was, will be, etc, was followed by the definite article the, as "I am the king" "that is the truth". etc.
§ 597. When is this verb is used? Whenever in the English sentence the verb "to be" is followed by (A) a proper name; or (B) a common noun, with the defnite article the, or (C) a common noun, with the possessives my, thy, his, her, our, your, their.
As (A) Is tú Cormac, you are Cormac; (B) Is tú an rí, you are the king; (C) Is tú mo ṁáṫair, you are my mother.
|Is mé||Is sinn|
|Is tú||Is siḃ|
|Is é (ish ae)||Is iad (ish ee'-ădh)|
|Is í (ish ee)|
These are the forms for I am, thou art, he is, she is, we are, you are, they are. Notice that the pronouns of the third person instead of being sé, sí, siad, have lost the s and are é, í, iad. These forms are now used after all part of is.
§ 599. There is some difference of usage in this matter. In the old language we often find is-sé, is-sí, is-siad and in the modern spoken language is sé, is sí, is siad are always said, often shortened to 'sé, 'sí, 'siad; But writers of Irish of the last two centuries have preferred to write is é, is í, is siad, and sometimes is inn, is iḃ.
§ 600. The EMPHATIC FORMS of the pronouns are mise (mish-ĕ), I myself; tusa (thus-ă) yourself; seisean (shesh'-ăn) himself; sise (shish'-ĕ) herself; sinn-ne or sinne (shin-ĕ) ourselves; siḃ-se (shiv'-shĕ) yourselves; siadsan (shee-ădh-săn) themselves.
N.B.—these forms are used, not when myself, etc would be used in English, but when the pronoun would be emphasised by a stress of the voice, as in the following familiar endings of stories: fuair mise an t-áṫ, agus fuair siadsan an cloċa; báiṫeaḋ (bau'hoo) iad-san agus ṫáiniġ mise slán: "I found the ford, and they found the stepping stones; they were drowned, and I came safe."
as in English