Practical necessity : a study in ethics, law, and human action




O'Brien, Matthew Bennett

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The dissertation is an examination of obligation, which I argue is a mode of rational necessity that is proper to human agency. I begin from G. E. M. Anscombe’s celebrated attack against modern moral philosophy, and then sketch a positive theory of obligation as it figures in morality and in law, drawing upon the work of Aquinas and Aristotle. The first chapter explicates this idea of “practical necessity” and the second chapter shows that Aristotelian ethics, because it is not a theological law conception of ethics, has no place for a peculiarly moral conception of obligation. The third chapter examines Aquinas’s conception of moral law and argues that Aquinas vindicates Anscombe’s negative critique of the “moral ought.” The fourth chapter shows that the application of exceptionless moral norms (i.e. moral absolutes), which is one kind of obligation, requires attention to aspects of social practices. Attention to social practices allows the resolution of controverted problems about specifying intentions and applying the principle of double effect in a way that makes exceptionless moral norms workable. The fifth and final chapter defends the conception of intentional action assumed in the fourth chapter, and demonstrates that the scholastic ‘sub specie boni’ thesis is an integral part of action explanation, as well as Anscombe’s notion of “practical knowledge”. The upshot of the dissertation is an integrated investigation into how the ideas of good and necessity figure in ethics, law, and human action.




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