In linguistic typology, active–stative alignment (also split intransitive alignment or semantic alignment) is a type of morphosyntactic alignment in which the sole argument ("subject") of an intransitive clause (often symbolized as S) is sometimes marked in the same way as an agent of a transitive verb (that is, like a subject such as "I" or "she" in English) but other times in the same way as a direct object (such as "me" or "her" in English). Languages with active–stative alignment are often called active languages.

The case or agreement of the intransitive argument (S) depends on semantic or lexical criteria particular to each language. The criteria tend to be based on the degree of volition, or control over the verbal action exercised by the participant.

For example, if one tripped and fell, an active–stative language might require one to say the equivalent of "fell me." To say "I fell" would mean that the person had done it on purpose, such as taking a fall in boxing. Another possibility is empathy; for example, if someone's dog were run over by a car, one might say the equivalent of "died her." To say "she died" would imply that the person was not affected emotionally.

If the core arguments of a transitive clause are termed A (agent of a transitive verb) and P (patient of a transitive verb), active–stative languages are languages that align intransitive S as S = P/O∗∗ ("fell me") or S = A ("I fell"), depending on the criteria described above.

Active–stative languages contrast with accusative languages such as English that generally align S as S = A, and with ergative languages that generally align S as S = P/O; that is, there are two types of S in active-stative languages. In ergative languages, some types of O/P can similarly be O/P=A.

For most such languages, the case of the intransitive argument is lexically fixed for each verb, regardless of the actual degree of volition of the subject, but often corresponding to the most typical situation. For example, the argument of swim may always be treated like the transitive subject (agent-like), and the argument of sleep like the transitive direct object (patient-like). In Dakota, arguments of active verbs such as to run are marked like transitive agents, as in accusative languages, and arguments of inactive verbs such as to stand are marked like transitive objects, as in ergative languages. In such language, if the subject of a verb like run or swallow is defined as agentive, it will be always marked so even if the action of swallowing is involuntary. This subtype is sometimes known as split-S.

In other languages, the marking of the intransitive argument is decided by the speaker, based on semantic considerations. For any given intransitive verb, the speaker may choose whether to mark the argument as agentive or patientive. In some of these languages, agentive marking encodes a degree of volition or control over the action, with the patientive used as the default case; in others, patientive marking encodes a lack of volition or control, suffering from or being otherwise affected by the action, or sympathy on the part of the speaker, with the agentive used as the default case. These two subtypes (patientive-default and agentive-default) are sometimes known as fluid-S.

If the language has morphological case, the arguments of a transitive verb are marked by using the agentive case for the subject and the patientive case for the object. The argument of an intransitive verb may be marked as either.