 The case against reductionism about internal relations has proceeded so far from a relatively a priori basis. But there’s also a case to be made against it on a posteriori grounds. Grant for the sake of argument the claim that if a relation is internal then it doesn’t count as an ontological addition. The significance of this claim, when it comes to providing an inventory of the world’s furniture, depends upon the extent to which relational truths have monadic foundations. But relativity theory, quantum theory and even classical mechanics provide an a posteriori basis for doubting that there are very many, if any, \(F\)s and \(G\)s capable of serving as monadic foundations for target \(R\)s, i.e., intrinsic properties to which a significant range of relations may be reduced.