 There is at least one further aspect of reduction that is overlooked by [the structuralist conception]. This is what I would like to call “the ontological aspect”. I wish to argue that, for a complete picture of a reductive relationship between two theories, one has to take into account some sort of relation between the respective domains. Otherwise, when confronted with a particular example of a reductive pair, we would feel that all we have is an ad hoc mathematical relationship between two sets of structures, perhaps by chance having the mathematical properties we require of reduction but not really telling something about “the world”. We could have a reductive relationship between two theories that are completely alien to each other. (Moulines 1984: 55)