Language works through relations of difference, then, which place signs in opposition to one another. Saussure asserted that there are only two types of relations: syntagmatic and paradigmatic. The latter is associative, and clusters signs together in the mind, producing sets: "sat", "mat", "cat", "bat", for example, or "thought", "think", "thinking", "thinker". Sets always involve a similarity, but difference is a prerequisite, otherwise none of the items would be distinguishable from one another: this would result in there being a single item, which could not constitute a set on its own.