Some generative linguists think that ill-formedness might be strictly additive, thus trying to figure out universal constraints by acquiring scalar grammaticality judgements from informants.
The grammaticality of the progressive passive, called by some the imperfect passive, was controversial among grammarians in the 19th century, but is accepted without question today.
Linguists draw a distinction, however, between grammaticality and acceptability: what may be considered grammatical across all dialects may nevertheless be considered not acceptable in certain dialects or contexts.
Generative grammar has been under development since the late 1950s, and has undergone many changes in the types of rules and representations that are used to predict grammaticality.