The important thing here is that there are two ways of marking the end of a line. You can do it with a rhyme, or you can do it with a pause. And in the tetrameter that second option is out the window. So all tetrameters have to rhyme. I wandered lonely as a cloud That floats on high o’er vales and hills When all at once I saw a host Of many dancing buttercups. Is just nonsense.
