O’Neill explains that she was both attracted and repelled by utilitarianism. On the one hand, she shared with utilitarianism the view that moral theory should be something precise and determinate that guides actions – that one should look for (as Rawls put it in the title of his very first published article) “a decision procedure for ethics”. Yet utilitarianism’s own decision procedure is one of ruthless aggregation. Kant’s moral theory, by contrast, looks to be a way of defending the individual from instrumental subordination to collective ends. It is, to use the Rawlsian technical term, deontological. Finally, Rawls and his students took for granted that a Kantian ethical theory must be as thoroughly secular and compatible with natural science as its utilitarian rival seemed to be. Hence they focused on Kant’s formulations of the categorical imperative as a “moral law” and not his – avowedly metaphysical – ideas about how human beings’ moral agency ties them to a “noumenal” realm of freedom.
From a review by Michael Rosen in The Times Literary Supplement of Acting on Principle: An Essay on Kantian Ethics (second edition), an updated version of the book written by Onora O’Neill in 1975.
A description, table of contents and introduction to the second edition is available on the Cambridge University Press website.