a fundamental flaw/weakness (=something basic that is wrong) Some people see this as a fundamental flaw in his argument. 根本的缺陷/弱点

fundamental changes We shall have to make some fundamental changes in the way we do business. 我们将不得不对我们做生意的方式做一些根本的改变。

fundamental difference There was an even more fundamental difference in attitude between us. 我们的态度甚至还有一个更根本的差异。

fundamental principle/issue/question A fundamental principle of Anglo-American law is that crimes must be clearly defined. 英美法律的一条基本原则就是，罪行必须得到明确界定。

My relationship with the actors is fundamental to my work as a director. 我和演员的关系对我的导演工作有重要影响。