 It is important to be clear on what we mean by “object” and “relation” in this context. As regards objects, all that matters from a structuralist point of view is that there are so and so many of them. Whether the objects are desks or planets is irrelevant. All we need are dummies or placeholders whose only property is “objecthood”. Similarly, when defining relations one disregards completely what the relation is “in itself”. Whether we talk about “being the mother of” or “standing to the left of” is of no concern in the context of a structure; all that matters is between which objects it holds. For this reason, a relation is specified purely extensionally: as a class of ordered \(n\)-tuples. The relation literally is nothing over and above this class. So a structure consists of dummy-objects between which purely extensionally defined relations hold.