If it is unusual for the properties of a relationship to remain constant over time, what do we mean by a “stable” relationship? Most relationships change progressively, or vary whilst remaining within certain limits, or change from one temporarily more or less constant state to another. Such changes or variations may be anything from trivial to so great that the new relationship has little in common with the old. An example of the latter would be a parent-child relationship. This starts with one set of interaction types, marked complementarity related to the gross differences in moral and cognitive levels, and gradually changes to something more like a peer-peer relationship with a different set of interactions, more reci procity and even reversed complementarity, and much greater similarity in moral and cognitive levels. There may be periods of discord and apparent change, but what emerges is in some ways a new relationship and in others still the same one. Clearly, then, stability is a relative matter, and how much change we allow without describing the relationship as a new one is an arbitrary matter.