Originally, the cardinals were parish priests and deacons of Rome and bishops of the suburban dioceses. This tradition had been symbolically preserved by appointing the cardinals as titular parish priests and deacons of Roman churches.
Once a church become a titular church, it remains so unless the Pope revokes the status, even if there is currently not a titular Cardinal attached to the church. When the status of titular church is given, it is specified whether it is a presbyterial or a deaconal title. At times, a Cardinal is promoted to the rank of Cardinal Priest, but still retains his titular deaconry, which is the promoted with him to a presbyterial title pro hac vice ("for the occasion").