Clitic climbing is a phenomenon first identified in Romance languages in which a pronominal object of an embedded infinitive appears attached to the matrix verb.
Pronominal objects in Romance languages are typically expressed as clitics.
The object pronoun, lo, a clitic, is attached to the infinitive in the embedded or subordinate clause in (1a).
Unknown glossing abbreviation(s) (help);Only clitics from embedded clauses in which the verb does not exhibit any aspectual morphology can climb to the matrix clause in Tagalog.
Unknown glossing abbreviation(s) (help);So, the sentence in (2b) is grammatical because the embedded verb, dalawin "to be visited", is not marked for any aspect, whereas the sentence in (3b) is ungrammatical because clitic climbing has occurred out of the embedded clause in which the verb, dinalaw "was visited", is marked for the perfective aspect.