有些动词可表达讯息的来源,本身的语义已足以表现出事件的真实性,例如guess(猜测)、wish(愿望)或promise(承诺),讲的显然都是尚未成真的事情,但是感官动词see、hear则传达“亲眼见、亲耳闻”的事件:
I guess he wrote a book. →猜测而已,不能当真
I think he wrote a book. →想想而已,没有根据
I saw that he was writing a book. →眼见为凭
——劉美君. (2012). 英文文法有道理! 重新認識英文文法觀念. 聯經.