Change can take place only when liberal and radical pressures are both strong. Intelligent liberals have always recognized the debt they owe to radicals, whose existence permits liberals to push further than they would otherwise have dared, all the while posing as compromisers and mediators. Radicals, however, have been somewhat less sensible of their debt to liberals, partly because of the rather single-minded discipline radicals are almost forced to maintain, plagued as they always are by liberal backsliding and timidity on the one hand and various forms of self-destructiveness and romantic posing on the other.... Liberal reforms and radical change are thus complementary rather than antagonistic. Together they make it possible continually to test the limits of what can be done. Liberals never know whether the door is unlocked because they are afraid to try it. Radicals, on the other hand, miss many opportunities for small advances because they are unwilling to settle for so little.