Why Humean constructivists should become Kantian constructivists.

One of the main reasons for philosophers to have embraced Humean constructivism rather than Kantian constructivism is a negative one: they believe that in the end Kantian constructivism is an unstable position. Their idea is that the Kantian constructivist can either choose to hold on to the idea of categorical reasons for action but in that case she has to be prepared to commit to (robust) moral realism (which both Humean and Kantian constructivists reject) or alternatively, she might reject (robust) moral realism but in that case she has to give up on the idea of categoricity. The aim of this paper is to defend Kantian constructivism against Humean constructivism and more specifically against recent objections raised by Sharon Street. I will do so by arguing that Kantian constructivism follows from formal, normative commitments that pertain to instrumental reasoning that Humean constructivists like Sharon Street themselves accept. More specifically I will argue that categorical reasons for action follow from applying the principle of instrumental rationality to the first-person perspective of an agent, provided that there are certain necessary means for action in general. From this follows, I will argue, that Humean constructivists should either become Kantian constructivists or that they have to become sceptics about normativity. [ABSTRACT FROM AUTHOR]