From Teflpedia

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.