Ergativity entails that the grammar give treatment to the subject (A) of a transitive verb that is differentiated from the treatment given to the object (O) of such a verb and the subject (S) of an intransitive verb, which are treated similarly to each other. Such differential treatment may take the form of a special case marker (such as an affix or a particle) used with A but not with O or S, or of a specific agreement pattern (for example, the verb may agree in person and number with A, but not with O and S).