Fluid-S

A fluid-S language is a language in which not so much subject and object are distinguished from each other but agent and patient. The subject of an intransitive verb is marked the same way as a transitive subject if it is an agent, and like a transitive object if it is not. Here are a few examples from Old Albic:

(1)	Ibretara o ndero am phath.
	AOR-break-3SG:P-3SG:A M-AGT man-AGT I-OBJ knife-OBJ
	?The man broke the knife.?

(2)	Obosca o ndero.
	AOR-flee-3SG:A M-AGT man-AGT
	?The man fled.?

(3)	Acara om nderom.
	AOR-sit-3SG:P M-OBJ man-OBJ
	?The man sat.?

Both markings may be used with the same verb, depending on the agency of the subject:

(4)	Acvamsa atto maso.
	AOR-come-3SG:A father-AGT 1SG-GEN-AGT
	?My father came.?

(5)	Acvama gratath thas.
	AOR-come-3SG:P letter-OBJ 2SG-GEN-OBJ
	?Your letter came.?

In the examples (2) and (4), the subject acts out of itself, it is an agent; hence it receives the same marking as the transitive subject in (1). The subjects in (3) and (5) are not agents, and are thus marked like the object in (1).

See also degrees of volition.