English grammar is so complex and confusing for the one very simple reason that its rules and terminology are based on Latin - a language with which it has precious little in common. In Latin, to take one example, it is not possible to split an infinitive. So in English, the early authorities decided, it should not be possible to split an infinitive either. But there is no reason why we shouldn't, any more than we should forsake instant coffee and air travel because they weren't available to the Romans.