1. He left before I returned. He went before I returned. Both are OK and mean the same. 2.He went where I told him to go. He left where I told him to go. The first one makes sense - the second doesn't. 3.If the plane left on time, they should be in New York now. If the plane went on time, they should be in New York now. The first is correct. The second is a bit lazy but the meaning would be clear enough. "To leave" as you have used it in your example means to "go away / depart". Sometimes you can just say "go" without "away" if the context indicates that the sense of "go" means "go away / depart".