Designations on the political spectrum

Then [1661] and ever since, men have tended to fall into four different general attitudes toward political policy: reactionary, conservative, liberal, radical. It is well to distinguish carefully among those terms; for they keep recurring and are often misapplied. The reactionary is one who wishes to go back to former conditions; the conservative, usually well contented with things as they exist, is psychologically or economically opposed to any considerable change; the liberal has a broadminded attitude, ready to preserve whatever seems to him good in the old, but equally ready to make changes which seem to him improvements; while the radical, as the Latin derivation indicates, desires to get  at the roots and start anew.

(from A History of England and the British Empire)