I want to ask about what is definitions about grammatical and ungrammatical according to English syntax. What is the effect to the our speech quality? Thanks for your advice. :)
closed as not a real question by user114, Persian Cat, snailcar♦, StoneyB, WendiKidd Mar 11 '13 at 20:02
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I looked up grammatical in NOAD, and the definition there confirmed my hunch:
grammatical (adj.) well-formed; in accordance with the rules of the grammar
So, what is grammatical? As snailplane said, asking for a complete list of grammar rules is asking too much from an answer, but some of the first ones that come to mind are subject-verb agreement, using the right parts of speech, and using words within their accepted range of definitions as defined by a dictionary. So, the statement:
If two nice people are already on the bus, and five more get on board, then there are now nine nice people on the bus.
is grammatically correct, even if it's mathematically wrong. However, this sentence has the opposite problem:
If two nicely people is already at the bus, and five more gets on board, then that constructs seven person on the bus.
because the verbs are conjugated wrong, the preposition at is misapplied, the word nicely should be in its adjective form, person in the expression "seven person" should be plural, and I haven't used the word constructs properly (even if I can say "that makes seven people on the bus", and even though "constructs" is a synonym of "makes").
Also, a sentence may be ungrammatical, but it can also be understandable. Humans don't process language the same way compilers do; if we read or hear something that is grammatically incorrect, we don't throw fits, and there's a good chance we'll still catch the intended meaning. For this reason, some sentences may not be grammatical, but they will still be acceptable informal speech, or something might fall outside the strict rules of grammar, but still be recognized or oft-used slang. So, is slang grammatical? I ain't goin' there.
Whether or not capitalization and punctuation rules fall under the umbrella of "grammar" is up for debate. I'll go so far as to say they are related in this context, but I won't say any more than that.
Perhaps this would have been a better meta question, I don't know. I think it's worth addressing, however. In a language forum, people will often ask, "Can I say this?" or "Is it correct to say that?" Words like "can" and "correct" are loaded terms – you can say anything you want to, but asking if something "is grammatically correct" or "understandable," or if it "sounds natural", or "is appropriate in a formal context," or if it is "polite" – those are five different questions that might have five different answers.