<p>What makes it true that we authoritatively ought to perform an action? I examine Humean constructivist answers to that question, according to which what makes it true that we authoritatively ought to perform an action is that we would, were we to reflect properly, have a certain kind of positive response toward performing the action. I distinguish two kinds of Humean constructivist views: substantivist and formalist. Substantivists believe there are substantive moral practical principles that proper reflection inevitably leads all of us to—moral principles with content, principles that prescribe particular types of action. Formalists deny that we are warranted in thinking that proper reflection will lead all of us to the same substantive moral principles; according to formalists, we can identify the form of authoritative oughts, but we cannot identify the authoritative ought with any particular moral content. I argue for the formalist version of Humean constructivism.</p>