Ruth Chang has argued for the existence of a fourth positive value relation, distinct from betterness, worseness and equality, which she calls “parity.” In an earlier article I seemed to criticize Chang's suggestion by offering an interval model for the values of items that I claimed could accommodate all the phenomena characteristic of parity. Wlodek Rabinowicz, offering his own model of value relations, endorsed one central feature of my proposal: the need to distinguish permissible preferences from required ones. But he, (...) along with Chang, correctly pointed out that my own model suffered from serious formal problems. The present article offers an improved interval model, but the main point is not the model itself. Rather, it is the derivation of the model from a response-dependent account of practical rationality. This derivation helps explain why we have a concept for which Rabinowicz's model is appropriate, and therefore supplements Chang's existence arguments. My conclusion is that we can take Chang's view, Rabinowicz's and mine as providing a reinforcing set of views. (shrink)