These words all describe sb/sth that is extremely important and completely necessary because a particular situation or activity depends on them. 以上各词均表示极其重要、完全必要、必不可少。

• essential extremely important and completely necessary, because without it sth cannot exist, be made or be successful 指极其重要的、完全必要的、必不可少的：◆Experience is essential for this job. 对于这个工作，经验是非常重要的。
• vital essential 指极其重要的、完全必要的、必不可少的：◆The police play a vital role in our society. 警察在我们的社会中起着极其重要的作用。

essential or vital? 用 essential 还是 vital？

These words have the same meaning but there can be a slight difference in tone. Essential is used to state a fact or opinion with authority. Vital is often used when there is some anxiety felt about sth, or a need to persuade sb that a fact or opinion is true, right or important. Vital is less often used in negative statements. 以上两词意义相同，但语气稍有区别。essential 用以说明事实或表明权威意见，vital 常用于对某事感到急迫或需要使人信服某一事实或意见确实、正确或重要等情况。vital 较少用于否定句：◆It was vital to show that he was not afraid. 最重要的是要表现出他毫无畏惧。◆Money is not vital to happiness.

• crucial extremely important because a particular situation or activity depends on it 指至关重要的、关键的：◆It is crucial that we get this right. 我们把这个问题弄明白是极其重要的。
• critical extremely important because a particular situation or activity depends on it 指至关重要的、关键的：◆Your decision is critical to our future. 你的决定对我们的将来至关重要。

crucial or critical? 用 crucial 还是 critical？

These words have the same meaning but there can be a slight difference in context. Critical is often used in technical matters of business or science; crucial is often used to talk about matters that may cause anxiety or other emotions. 以上两词意义相同，但使用场合稍有区别。critical 常用于商业或科学的技术问题，crucial 常用于可能引起焦虑或其他情感方面的问题。

• decisive of the greatest importance in affecting the final result of a particular situation 指决定性的、关键的：◆She has played a decisive role in the peace negotiations. 她在和谈中起了关键作用。
• indispensable essential; too important to be without 指必需的、不可或缺的：◆Cars have become an indispensable part of our lives. 汽车已成了我们生活中必不可少的一部分。

Patterns

• essential/vital/crucial/critical/decisive/indispensable for sth
• essential/vital/crucial/critical/indispensable to sth
• essential/vital/crucial/critical that…
• essential/vital/crucial/critical to do sth
• a(n) essential/vital/crucial/critical/decisive/indispensable part/factor
• of vital/crucial/critical/decisive importance
• absolutely essential/vital/crucial/critical/decisive/indispensable