A tripartite language, also called an ergative-accusative language, is one that marks the agent, experiencer, and patient verb arguments each in different ways. If the language has morphological case, the arguments are marked in this way:

• the agent is marked with the ergative case
• the experiencer is marked with the intransitive case
• the patient is marked with the accusative case

In simpler terms, it distinguishes between the subject of an intransitive verb, the subject of a transitive verb and the object (of a transitive verb).

Languages lacking case inflections may indicate case with a fixed word order.

Tripartite languages are rare. Some examples are Indo-Aryan, Wangkumara, Nez Percé and Kalaw Lagaw Ya. Several constructed languages, especially engineered languages, use a tripartite case system or tripartite adposition system.