If the attack is to be finally repulsed it will be imperatively necessary for the libertarian to maintain that no full explanation of the physical universe can ever gain assent which does not take account of the reality and influence within the material world of human power of initiative and freedom.
The commercial production of sulphuric acid imperatively requires that the nitrogen oxides (which originally were always introduced in the shape of nitric acid) should be available as long as possible, before being lost mechanically or by reduction to the inactive forms of nitrous oxide or elementary nitrogen.
In the last quarter their victims were British subjects, and at last it became imperatively necessary to check their advance.
In the Agnus Dei the circumstances of the time gave him something special to say which has never so imperatively demanded utterance since.
The text of the Dies Irae so imperatively demands either a very dramatic elaboration or none at all, that even in the 16th century it could not possibly be set to continuous music on the lines of the Gloria and Credo.