REVOLUTION. A radical and generally violent effort to overthrow a civil government or constitution. Essential to a revolution is that the change of regime is not brought about by peaceful evolution or mutual agreement between the power that withdraws and the power that takes over the new government. Revolutions are caused either by the masses or by an act of high officials in the government. In the latter case it is called a coup d'état. In the twelfth century John of Salisbury (1115-80), followed by others, held that the murder of a tyrant was permissible even by a private citizen. The thesis was condemned by the Council of Constance in 1415 (Denzinger 1235), and by Pope Paul V in 1615 (constitution Curia Dominici Gregis).