Logic is an essential part of our rational behaviour, and that its significance and the meanings of its concepts cannot be understood by ignoring the kind of actions the speakers use logical terms for. There is no isolated problem that logic poses to the project of naturalism. Inferential practices are just a kind of linguistic actions. If the latter are naturalistically explainable, so are the former. We will focus on logical connectives and quantifiers as higher order expressions. Some traditional treatments of logical constants only point, dimly, to their higher order status. • The Medieval characterization as syncategorematic terms • Invariantist positions that stress that logical constants don’t discriminate among individuals • Inferential accounts to the extent that logical constants exhaust their meaning in their introduction and elimination rules Applying to them the understanding on higher order concepts reached by contemporary philosophy of language might offer a healthy change of perspective towards this, traditionally troublesome, issue. The particular aspect of this general research on which we will search some illumination during our stay at the KLI has to do with the cognitive human abilities that can account for human trading with higher order concepts. A further and related topic we will be concern with the kind of a priori proper of logic, once logical constants have been understood as higher order concepts.