In all political discussions we must assume agreement in ultimate judgments of value, and our hope of converting an opponent must lie in showing him either (1) that his general political theories contradict the ethical principles that we have in common, whilst ours are compatible with them, or (2) that his measures are not likely to lead to the results which we agree would be desirable if they could be reached. The fruitlessness and heat of political discussion spring largely from the confusion of matters of fact with matters of value.

(C. D. Broad, “Lord Hugh Cecil’s ‘Conservatism’,” International Journal of Ethics 23 [July 1913]: 396-418, at 399)