In this paper, I argue that hinge propositions are ways of acting that constitute abilities or skills. My starting point is Moyal-Sharrock's account of hinge propositions. However, Moyal-Sharrock's account leaves gaps to be filled, as it does not offer a unified explanation of the origin of our ungrounded grounds. Her account also lacks resources to respond to the issue of demarcation, since it does not provide a criterion for distinguishing ways of acting that can legitimately fulfill the role of ungrounded (...) grounds from those that cannot. Without an answer to this issue, the relativistic threat is serious. I then propose that by narrowing the ways of acting to those that are constitutive of abilities, we can deal with the relativistic threat. I provide an ecological approach to abilities through which I explain why abilities are reality-soaked and therefore why the ways of acting that constitute them are legitimate ungrounded grounds. Based on that approach, I provide an answer to the issue of demarcation that defuses the relativistic threat. (shrink)