What is the difference among "because," "since" and "as"? I do not know which is the best, though it depends on a context. For example: 1. Thurgood Marshall passed the bar exam at the first try, BACAUSE he studied hard. 2. Thurgood Marshall passed the bar exam at the first try, SINCE he studied hard. 3. Thurgood Marshall passed the bar exam at the first try, AS he studied hard. Thank you for reading! (Large letters are intentional.)