indispensable、essential、necessary与requisite这些形容词均有“必不可少的、必需的”之意。
indispensable : 语气强,侧重指绝对必要性或不可缺少性。
- This book is an indispensable resource for researchers.
这本书是研究者必不可少的资料。 - His long experience at the United Nations makes him indispensable to the talks.
在联合国长期的工作经验使他成为谈判中不可或缺的人物。
essential : 指对事物本身性质具有决定性的重要性,暗含不可缺少,否则便无法存在。
- Government support will be essential if the project is to succeed.
这个项目能否成功,政府的支持至关重要。 - There is essential work to be done before the building can be re-occupied.
这座楼在重新入住前必须进行必要的维修。 - Water is essential for/to living things.
水对于生物来说是必不可少的。 - It is essential (that) our prices remain competitive.
我们保持价格方面的竞争优势是至关重要的。 - For the experiment to be valid, it is essential to record the data accurately.
要保证实验的有效性,就必须精确地记录数据。
necessary : 最常用词,侧重由客观因素决定的某种需要,强调不可避免,但并非绝不可缺少。
- He lacks the necessary skills for the job.
他不具备做这项工作所需的技能。 - I don't have much time so I won't be staying any longer than necessary.
我时间不多,所以若非必要我不会逗留。 - Just do what's necessary and then leave.
做完必要的事情就走吧。 - If necessary, we can always change the dates of our trip.
必要的话,我们随时可以改变旅行的日期。 - Is it necessary for all of us to be present at the meeting this afternoon?
我们必须全体出席今天下午的会议吗? - We don't want to take any more luggage with us than is strictly necessary.
除了必不可少的行李以外,我们不想带多余的东西。
requisite : 正式用词,特指为实现某一目的或得到某种结果而应有的需要,有时可与necessary换用。
- He lacked the requisite skills for the job.
他缺少从事这项工作所必需的技能。 - The requisite number of countries have now ratified the convention.
批准这项条约的国家已经达到了规定的数目。