The Indeterminacy Thesis and the Normativity of Practical Reason

This paper argues against the indeterminacy thesis that attempts to defeat traditional natural law by asserting that specific moral norms cannot be based on human nature. As put by Jean Porter : “the intelligibilities of human nature underdetermine their forms of expression, and that is why this theory does not yield a comprehensive set of determinate moral norms, compelling to all rational persons.” However, if this were so, one could adopt any morality with impunity from nature’s sanctions. But I argue that nature punishes violators of the natural law in various ways. In addition, I argue that the indeterminacy thesis cannot be supported by appealing to the diversity of moral norms across the globe. Such diversity is required, for instance, both by the reliance of Thomistic natural law on the practical syllogism and by its reliance on practical reason’s ability to prescribe for the sake of the person in highly unique situations as required by Wojtyla’s Personalistic Norm and Aquinas’s norm of neighborly love.