According to Devarim 18:11 we are forbidden to beseech the dead. However, there is a long Jewish tradition of visiting the graves of tzadikim who have died and asking that the tzadikim petition G-d on our behalf. Every time I look for an explanation of why this is permissible, I read something different. (For example, that a Jew may serve as an intermediary between another Jew and G-d; that our conversation with the tzaddik is understood as unilateral and therefore is not "beseeching"; that we are only asking G-d to have mercy on us for the sake of the tzadikim; and many other miscellaneous explanations, such as the handful listed here.) All this seems a bit like we're trying to explain away a practice we just really, really want to do and have a tradition of doing, despite the fact that it is is prohibited by Torah. So, what is the "canonical" explanation for why one may beseech a dead Jewish tzaddik, if indeed one may?
Related: Speaking to a deceased person