The answer to the vexed question regarding whether there is such a thing as correct grammar is very clearly that there is. But, having said that, most of the common disputes, such as whether it is correct to start a sentence with a conjunction, seem to be unnecessary. My feeling is that most of the problems in the use of language are not syntactic or morphological and most disputes can be adjudicated by referring to a style guide such as Fowler’s Modern English Usage.

Errors tend to be in orthography, that is, spelling and punctuation, and vocabulary, particularly through choosing one word where another is meant or choosing a word but misunderstanding its meaning. As an example, the frequent use of different to instead of different from looks like a misunderstanding of meaning rather than a syntactical error, because difference is a movement away from rather than a movement towards.

The basic grammatical template is relatively simple and robust and for the most part an ungrammatical statement will be too ambiguous or too hard to decode to be meaningful. Syntax and morphology are, like systems of measurements, historical cultural constructs. As cultural constructs they are artificial and in a sense arbitrary. However, as historical constructions they are not owned by anyone. They are common property and widely shared and for that reason very stable.

Grammatical rules are normative in the way that the rules of the road or the rules for the conduct of meetings are normative. They serve a purpose and if they no longer serve that purpose they evolve. Conversely, they don’t change if there is no pressing need. One of the reasons that grammar is stable is that it doesn’t need to change. There is sufficient flexibility within the existing structure to accommodate any currently conceivable data model.

This means that syntax doesn’t constrain semantics. What might constrain semantics is the absence of a useful vocabulary, but the language is easily and almost infinitely extendible in the classes of words where this is important. Another way of putting this would be to say that grammatical errors are always unnecessary; there is no meaningful statement that cannot be constructed using the syntax and morphology described here.

However, grammar does evolve and that evolution may lead to what was once regarded as an error becoming idiomatic. The use of the subjunctive is a good example. In the past tense it still sounds natural but in the present tense has become either pedantic or facetious. The subjunctive mood is falling out of use in idiomatic English for a number of reasons. One possible reason is that the subjunctive isn’t strictly necessary to avoid ambiguity. The sense is clear from the meaning of the words. A second reason may be that there is no rule which says that a particular mood should be distinguishable morphologically in a language. Distinctions can be made syntactically or morphologically in some languages that can only be made semantically in English. For example, English lacks the conditional mood or the future tense that is present in French. Similarly, French lacks the continuous aspect which is a characteristic of idiomatic English.