pledge和promise

Pledge(發誓、允諾)：if you pledge to do something, you promise in a serious way to do it! 你發誓要做某事，就表示你嚴肅地承諾要去做。如：I pledge that by next year we will have the issue solved. 我發誓明年前一定把問題解決。
Promise(承諾)：if you promise you will do something, you are saying that you will definitely do it. 你承諾要做某事，就表示你一定會去做。如：Promise me you will not waste your time. 跟我保證你不會浪費時間。
小結：pledge的程度較強烈(發誓)，且政治人物常用；promise(承諾)的程度較輕，日常生活常用，且Promise常常沒有兌現。