Register describes the choices made by the user. These choices depend on three variables. These are the field, tenor, and mode of discourse.
Field of discourse
Field refers to the subject matter or content being discussed. It is what the participants are engaged in discussing. In every discourse, there must be a subject matter or topic of discussion. For example, advertising, banking, and medicine.
Tenor of discourse
Tenor refers to the participants in discourse, their relationship with each other, and their purpose. It includes the style used by those taking part in the exchange. The choice of words is influenced by the relationship of these participants, the time, place, and purpose of the discussion. The styles could be formal or informal. These distinguish the registers used. While the formal style is used in the official settings (e.g., offices), the informal style is used in informal settings (e.g., home).
Mode of discourse
This refers to the channel of language use or the use to which language is put. It is the medium of discourse being used by the participants. This could be the written or spoken forms of discourse. Mode is an important aspect of discourse as it influences perception, meaning, and reaction.