Student or Learner
I wonder there is any difference (as interjections only, regardless of other parts of speech) between "hi" and "hello", "goodbye" and "farewell" or not.
What is the contexts to use each one ?
At least do they bring to the listeners different emotions ?
Thank you so much !
Hi is more informal, but there is nothing "formal" or stilted about "hello" either. Equal.
Goodbye and Farewell are the same thing; farewell is a bit more "old fashioned" but nothing is wrong with its use. It's a bit more poetic. Some consider either of these to be rather final. My partner, for example, doesn't like me to say "goodbye" when he leaves on an errand. It sounds, to him, like we'll never see each other again. We use more informally, "See ya!" (I'll see you again, soon.)
The difference in these words (your four examples) is almost entirely in the inflection, or spirit, in which they are spoken. You can use either Hi or Hello in a tone of voice that shows genuine excitement or total boredom at the encounter, for example. And Goodbye or Farewell can be reluctant, sad, or good riddance!, depending on your tone.