Q. 1. What is the Doctrine of Concomitance?
A. 1. The "doctrine of concomitance" holds that when receiving Holy Communion, we receive the whole Christ, body, blood, soul and divinity, under the form of bread alone. As such, it is not necessary to also receive the cup (Blood of Christ). The Body and Blood of Christ coexist in the Eucharistic Bread.
I remember a situation where a man used to go to Mass on a regular basis at a location where a few religious sisters also attended Holy Mass. The religious sisters always received Communion under both kinds, the Body and Blood of Christ. The man never accepted the Blood of Christ. I guess this must have annoyed one of the religious sisters. So one day she asked him, "How come you never accept Holy Communion under both species?" The man answered, "One Jesus is enough for me. I do not need two." In other words, the fullness of Jesus is found in both species, the Body and Blood of Christ.