"A progressive is always a conservative; he conserves the direction of progress. A reactionary is always a rebel."

The term "reactionary" is generally used as a term of offence, just as the term "progressive" is used as a term of praise; but only once in a hundred times is either of them used so as to convey any meaning or truth. Yet though the words have become a mere hackneyed cant, they have their proper use. Progress means persistence in the direction of one object maintained for a considerable period; reaction means some upheaval of disgust or contradiction, which overthrows the recent persistence and appeals back, perhaps, to its opposite. Thus we might truly say that English poetry from Cowley to Akenside progressed towards clearness and metrical accuracy. And we might truly say that Coleridge's Ancient Mariner was a reaction against this progress, the writing of a mere mad ballad in order to show how much more life there was in the old barbaric mysticism than in the recent easy-going rationality. Progress happens, in short, whenever men can endure one tendency for a long time. And reaction happens whenever some particular man can endure it no longer. These definitions are simple but I believe them to be comprehensive. A progressive is always a conservative; he conserves the direction of progress. A reactionary is always a rebel.

-Introduction to Past and Present by Thomas Carlyle (1909)