Liberalism is often criticized as too moralistic and removed from the realities of politics; and too complacently accepting of injustices. Such criticisms, familiar among contemporary political theorists, were expressed far more forcefully in the earlier twentieth century. Liberalism then came under attack from anti-liberals who wholly rejected the institutional and ethical limits on the political deployment of violence and fear insisted upon by liberals. Such anti-liberals advanced arguments for political ruthlessness on behalf of a truer morality - either the morality of pursuing morally imperative political goals; or the morality of "realistically" responding to threats to public order. Liberals found themselves faced with a dilemma: to adhere to their principles at the price of hampering their ability to combat both existing injustices, and the threat posed by ruthless anti-liberal movements; or to abandon their scruples in seeking to defend, or transform, liberal society. The criticisms and challenges confronting liberalism between the end of World War I, and the end of the Cold War, thus centered on opposing responses to problems of political ethics. They were also shaped by opposed ideals of political ethos - the "spirit", dispositions of character, sensibility and patterns of perception and response, which characterize the way in which actors pursue their values and goals in practice. In this dissertation I reconstruct these debates, and explicate the ethical claims and questions involved, presenting accounts of the opposed - yet often convergent - positions of moral purism, end-maximalism, and realism. I offer accounts of the ethical arguments and ethos of such anti-liberals as Lenin, Trotsky, and Lukacs; and explore the ambivalent commitments and ambiguous arguments of Max Weber, who influenced both critics and defenders of liberalism. Finally, and primarily, I reconstruct the ethical arguments and ethos of "tempered liberalism" - a strain of liberalism, represented by Reinhold Niebuhr, Isaiah Berlin, and Adam Michnik, which sought to re-imagine liberalism as an ethos which rejected both the innocence and complacency of some earlier liberalisms, and the ruthlessness of anti-liberalism, and steered a "moderate" ethical path between hard-headed, skeptical realism, and values of individual integrity and idealism. / Government