When do we use bidh and when bhi?
Edited to remove stupid answer.
Bidh and bhi are both future tense. Bidh - positive - will be. Cha bhi - negative - will not be. Am bi - interrogative - will it be?
The past tense equivalents are bha, cha robh and an robh.
Sorry I was confused, my mistake, I have edited out the misleading answer.