The verb bí in relative clauses
In relative clauses, in the present tense, the verb bí appears as 'atá' or 'nach bhfuil'.
Feicim an bia atá ar an mbord.
All well. Now, in the past tense, is it 'a raibh' or 'a bhí'? I encounter both. Is there any difference? Has this confused anyone else?
Chonaic mé an bia a raibh ar an mbord, a bhí ar an mbord.
Irish has two types of relative clauses: direct and indirect. Direct relative clauses use the independent forms of bí, e.g. atá or a bhí, and indirect relative clauses use its dependent forms, e.g. a bhfuil or a raibh. Note that a lenites in a direct relative clause, but eclipses in an indirect relative clause. (For negative relative clauses, nach and dependent forms are used in both types.)
An indirect relative clause is used if the clause is genitive or prepositional in nature, e.g. an bia a bhfuil a blas searbh (“the food whose taste is bitter”), an bord ar a raibh an bia leagtha (“the table on which the food was set”). Since your example sentence’s relative clause is neither genitive nor prepositional in nature, it would use the direct a bhí in the past tense.
Note that the rules for bí (which also apply to abair, déan, faigh, feic, and téigh) differ somewhat from those of other verbs; most verbs use ar rather than a for past-tense indirect relative clauses, and nár rather than nach for negative past-tense relative clauses of both types. Both ar and nár lenite.
The verb lean uses a leanas rather than a *leanann in positive direct relative clauses.
Is has its own rules, using combined forms of the relative particle and the verb:
|relative clause||present, before consonant||present, before vowel||past/conditional, before consonant||past/conditional, before vowel|
All of the past/conditional forms above lenite.