若做一個簡單劃分，between 是講兩者之間 (e.g. I am standing between the two trees)。 among 是三者或多是於三者, 即是一群人或物之間 (e.g. I am standing among the trees)。
不過，between 這字也會用於多於兩者之間。當一些人或物當中，要比較或強調其中任何兩者以上的不同，便要用 between 而不用 among 了 :
例如:
The differences between English, Chinese, and Arabic are significant.
She chose between MIT, Harvard, and Stanford, three very different universities
然而，among 是用於在一群人或物之間而沒有去區分這些人或物 。
例如:
I found the letter among his papers.
She chose among the top universities around the world.
More differences:
http://www.quickanddirtytips.com/education/grammar/between-versus-among?page=1
among vs. amongst:
http://www.quickanddirtytips.com/education/grammar/between-versus-among?page=2
Sources:
http://www.quickanddirtytips.com/education/grammar/between-versus-among
http://grammar.about.com/od/alightersideofwriting/a/Among-And-Between.htm
心智圖詞彙攻略: https://bit.ly/31rvaFL