Therefore no other person, even if he be a priest, may add, remove, or change anything in the liturgy on his own authority. 23. That sound tradition may be retained, and yet the way remain open to legitimate progress, careful investigation is always to be made into each part of the liturgy which is to be revised. This investigation should be theological, historical, and pastoral. Also the general laws governing the structure and meaning of the liturgy must be studied in conjunction with the experience