Innovation in metric is not to be measured solely by the width of the deviation from accepted practice. It is a matter of the historical situation: at some moments a more violent change may be necessary than at others. The problem differs at every period. At some times, a violent revolution may be neither possible nor desirable; at such times, a change which may appear very slight, is the change which the important poet will make. The innovation of Pope, after Dryden, may not seem very great; but it is the mark of the master to be able to make small changes which will be highly significant, as at another time to make radical changes, through which poetry will curve back again to its norm.
[From "In Memoriam". 1936.]