The final irregular verb is bí. This is one of two words that cover the functions of English ‘be’; the other will be taken up in the next unit. Bí is the imperative form; its plural is bígí.
The present tense of bí has the independent form tá and dependent form fuil, which is eclipsed after an, nach, go. Ní contracts with fhuil (fh being unpronounced) and is written níl, giving
Tá sé tinn. He is sick. Níl sé tinn. He is not sick. An bhfuil sé tinn? Is he sick? Nach bhfuil sé tinn? Isn’t he sick? Sílim go bhfuil sé tinn. I think that he is sick. Sílim nach bhfuil sé tinn. I think that he isn’t sick.