Please note, sarcasm can be a tone or a form of humour in the context of Language Analysis (often both).

Definition and effect on reader

Sarcasm is a remark which is sharp, bitter or cutting (often a bitter gibe or taunt). In spoken English it is generally identifiable by a person’s tone, but when written it is apparent when a statement is so clearly in opposition to the writer’s viewpoint that it must be ironic.

In this way, sarcasm can be used to mock (for example, to make an opposing view point seem foolish) and as a form of humour can serve to re-position the writer.