In linguistics, switch-reference (SR) describes any clause-level morpheme that signals whether certain prominent arguments in 'adjacent' clauses are coreferential. In most cases, it marks whether the subject of the verb in one clause is coreferent with that of the previous clause, or of a subordinate clause to the matrix (main) clause that is dominating it. Meanings of switch-reference The basic distinction made by a switch-reference system is whether the following clause has the same subject (SS) or a different subject (DS). That is known as canonical switch-reference. For purposes of switch-reference, subject is defined as it is for languages with a nominative–accusative alignment: a subject is the sole argument of an intransitive clause or the agent of a transitive one. It holds even in languages with a high degree of ergativity. The Washo language of California and Nevada exhibits a switch-reference system. When the subject of one verb is the same as the subject of the following verb, the verb takes no switch-reference marker. However, if the subject of one verb differs from the subject of the following verb, the verb takes the "different subject" marker, -š (examples from Mithun 1999:269): The Seri language of northwestern Mexico also has a switch-reference system which is similar in most ways to those of other languages except for one very salient fact: the relevant argument in a passive clause is not the superficial subject of the passive verb but rather the always unexpressed underlying subject. In clauses with subject raising, it is the raised subject that is relevant. Non-subject switch-reference The nominative subject is not always marked by switch-reference. For instance, many clauses, including those with impersonal or weather verbs, have no subject at all but can both bear and trigger switch-reference. Non-canonical switch-reference In addition, many languages exhibit non-canonical switch-reference, the co-referents of arguments other than the subject being marked by switch-reference. Here is an example from Kiowa (Watkins 1993): In this case, the use of the same-subject marker gɔ rather than the switch-reference marker nɔ indicates that the two subjects wrote letters at the same time, to the same person, and with the same subject (Watkins 1993). Form of switch-reference markers Switch-reference markers often carry additional meanings or are at least fused with connectives that carry them. For instance, a switch-reference marker might mark a different subject and sequential events. Switch-reference markers often appear attached to verbs, but they are not