Acceptability is the degree to which mastery-level speakers of a language (typically native speakers) accept that utterances are linguistically well-formed and appropriate in the given mode and context. If they are inappropriate they are an error.
Acceptability is typically measured by academics by presenting utterances to a group of native speakers and asking for their responses. What may be acceptable to one individual (a personal acceptability) may not be acceptable to other members of a group as a whole.
For example, the following sentence would typically be accepted by some but not all native English speakers:
- "I came into the room and found the cat sat on the chair"
EFL teachers typically do not have scientific procedure to check acceptability. They have to determine the acceptability of a sentence, often in real time against their own limited understanding of language.