(By Alena Witzlack-Makarevich): "The term ‘labileʼ is the most commonly used label for verbs which can be used transitively or intransitively without any formal change. A distinction is made between patient lability, more commonly referred to as P-lability, and agent lability or A-lability. P-lability stands for patient-preserving lability, that is, the P argument is preserved in the intransitive construction, as in I broke the stick[P] / The stick broke. A-lability stands for agent-preserving lability, that is the A argument is preserved in the intransitive construction, as in John[A] drinks tea / John drinks. ❡
This question asks only about P-labile verbs. Semantically, two things can happen with P-labile verbs. In case of (a) argument structure modifying P-lability, an otherwise transitive verb is used in the intransitive construction encoding an argument structure from which the A argument of the transitive construction is absent. In case of (b) less common argument structure preserving P-lability, the verb in its intransitive use implies the same participants with the same roles as in its transitive use, but in the intransitive use, the A argument is not expressed and is interpreted as non-specific."
In the Grammaticon, the term "labile" is restricted to what has been called "P-lability", because otherwise it would be too broad.