What is the distinction between Cardinal bishops, Cardinal priests and Cardinal deacons?
The origins of the cardinalate lie in the beginnings of the Diocese of Rome, when only the Roman clergy elected their new bishop. The Roman clergy of that time consisted of the Pope, six other bishops, the parish priests, and seven deacons. When the Church decided to use a more universal voice to elect the pope, some of these offices (those of the cardinal priests) became merely titular in order to have cardinals from dioceses all over the world, whlie the cardinal bishops are, I believe, still residents of the traditional parishes within Rome. Thus Francis Cardinal George, Archbishop of Chicago, is technically also the pastor of a parish within the Diocese of Rome.