Yitzchak's Blessings
After Yitzchak grants Yaakov (thinking that he is Esav) a bracha of prosperity and leadership, the real Esav arrives and begs his father for another blessing (see 27:34,36). Yitzchak's first response is that the special blessing which he intended for Esav (prosperity and power) had already been given to Yaakov (27:35,37). There is no other bracha for Esav, for he is obviously not suitable to receive the bracha of spirituality, intended for Yaakov. However, since Yitzchak still assumes that both sons are chosen, in the end he is able to grant Esav another bracha instead.

[This extra blessing ("tal ha'shamayim u'shmaney ha'aretz"/ see 27:38-39) includes prosperity, for this can be shared by both brothers. However, since the blessing of political leadership ("hvei gvir l'achicha..." /see 27:29) can only be given to one son, Yitzchak tells Esav that he will be able to obtain this blessing only should Yaakov fall (see 27:40).]

What about the bechira? When does Yitzchak find out the 'truth?'