In some languages, like Latin or Esperanto, you have the freedom to put words in different orders because case endings or other language features can make your meaning clear. In other languages, like Old English, word order is essential to the meaning of a sentence. “The man poisoned the bug” does not mean the same thing, for instance, as “The bug poisoned the man.”
In “The bug poisoned the man,” bug is the subject, the one doing the poisoning; poisoned is the verb; and man is the object, the unfortunate one being poisoned. This is an example of subject-verb-object word order. In contemporary old English, subject-verb-object is used the majority of the time in declarative statements. Other parts of the sentence may appear in various locations (“On Tuesday the bug poisoned the man” and “The bug poisoned the man on Tuesday,” for instance, are both correct), but in general, the subject must come before the verb and the object must come after the verb.
In Old English, however, the rules were different. But some linguists believe that it was primarily what they call a V2 language. A V2 language is one in which, in ordinary declarative statements, the verb must be the second major part of the sentence, while the order of the rest of the words is flexible.
So for instance, if contemporary English were V2, “On Tuesday poisoned the man the bug” might be correct, since the verb, poisoned, is the second part of the sentence after On Tuesday. Meanwhile, “On Tuesday the bug poisoned the man” might be wrong, since poisoned appears third, after On Tuesday and the bug.
Still, the old V2 structure shows up in specific declarative grammatical constructions in contemporary English. If you are an English language learner, check out the following list to start learning some of the more advanced rules of English grammar. If you are a native speaker, check it out and be wowed by all the complex rules you use every day without even thinking about it.
They are going to the party, and so are we.
For that second part of the sentence, we is the subject and are is the verb – yet if you put the subject before the verb, you’d get “They are going to the party, and so we are.” That either means something different (maybe “We are going to the party because they are?”) or is just grammatically incorrect, and either way, it sounds awkward if you don’t stick with V2 order.
Not once have I asked you for money.
“Not once I have asked you for money” would include the standard subject-verb-object order – but it would also be wrong.
Only in New York can you do such a thing.
“Only in New York you can do such a thing” – again, the standard word order would actually make this sentence incorrect.
Down the road came a green car.
“Came a green car” wouldn’t be right, but add Down the road to make came the second part of the sentence, and suddenly putting the verb before the subject sounds fine.
In truth, no one is 100% sure why English has so complicated a set of rules for word order. Recognizing it, though, can help you develop an appreciation for what a beautiful mess the English language is.