An indexical behavior or utterance is one whose meaning varies according to context. For example, 'That's very funny' normally means that something is funny. If it is said in a sarcastic tone, on the other hand, it means the opposite. The sociologist Harold Garfinkel uses the concept of indexicality as one of the key assumptions of his school of ethnomethodology. He assumes, in other words, that in social life all behaviour and discourse is theoretically indexical. It is the sociologist's job to provide the context such that the action or speech can be understood. See contextualism, thick description.