Conditionals are used to express both real, likely and unreal situations. As a result, tenses used with them are not flat; they change. That is why the difference between ‘If I arrive’ and ‘If I had ...

You know how the joke begins: “A guy walks into a bar…” But wait, for you to know the punch line, this has to be past tense. So wouldn’t it be, “A guy walked into a bar…?” It could be. But usually it ...