Certain relationships generate associative duties that exhibit robustness across change. It seems insufficient for friendship, for example, if I am only disposed to fulfil duties of friendship towards you as things stand here and now. However, robustness is not required across all variations. Were you to become monstrously cruel towards me, we might expect that my duties of friendship towards you would not be robust across that kind of change. The question then is this: is there any principled way of distinguishing those variations across which robustness of the disposition to fulfil duties of friendship is required from those across which it is not? In this paper I propose a way of answering this question that invokes distinctions concerning how we value friends and friendships, and how persons and friendships possess value – distinctions that are central to the project of specifying not only the limits of robustness, but also the source of duties of friendship and associative duties more generally.