1. 必要的，必需的　 essential for a purpose; that cannot be done without or avoided
2. 必然的，不可避免的　 that must be; inevitable

　～ actions　必要措施
　～ apologies　必要的道歉
　～ arrangements　必要的安排
　～ end　必然的结局
　～ equipment　必要的装备
　～ information　必要的信息
　～ instruments　必要的仪器
　～ makeshift　必要的权宜之计
　～ restriction　必要的限制
　～ result　必然的结果
　～ skill　必需的技能
　～ sum　所需的数目
　absolutely ～　绝对必要
　highly ～　非常必要的
　really ～　真的必要
　～ for　对…是必要的
　～ for health　对健康是必要的
　～ to　对…是必需的

　My money came short of the necessary sum.　我的钱不足所需的数目。
　Do you have the necessary skills for this job?　你具备做这项工作所必需的技能吗?
　They joined the wires and made the necessary new connection.　他们把电线接了起来，接通了所需的新线路。
　I'll leave it to you make the necessary arrangements.　我将让你作出必要的安排。
　The lawyers will draw up all the necessary papers.　律师们将拟定出所有必要的文件。
　No one foresees how the necessary restriction of the population will be effected.　任何人都无法预知将如何实现对人口的必要限制。
　They will meet in Beijing to debate taking necessary actions against environmental pollution.　他们将在北京会晤并讨论采取必要措施防止环境污染。

　A year's guarantee on the television set for all repairs might be necessary.　必须为电视机提供为期一年免费修理的保单。
　A climber must learn to discriminate as to when compass bearings are necessary and when they are not.　一个登山者必须学会辨别什么时候需要罗盘测定方位，什么时候不需要。
　Under certain conditions, answering back sarcastically is necessary.　在某种情况下，反唇相讥是必要的。

　Patience and understanding are necessary for a teacher of infants.　耐心和理解是幼儿教师必不可少的。
　What is necessary for one person is not always necessary for another.　对某人来说是必需的东西，对别人则未必如此。
　These reference books are necessary to scientists.　这些参考书是科学工作者所必需的。
　Sleep is necessary to one's health.　睡眠对健康是必要的。

　It was necessary to jump on the ice coated mounds of brush several times before they could flush.　你得在这些被冰覆盖的树丛上跳上好几下，才能把它们惊起。
　It's necessary to raise wages on the basis of increasing production.　需要在增加生产的基础上增加工资。
　Because the company was doing more business, it was necessary to expand the factory.　由于公司业务的扩大，扩大工厂是必然的。
　It was necessary to retire several generals who lacked energy and enterprise.　使几位缺乏精力和上进心的将军解职是必要的。
　It is sometimes necessary to indulge a sick child.　迁就一个生病的小孩有时是必要的。
　It is both important and necessary to note this difference.　注意到这个差别是重要的和必要的。
　Is it really necessary for me to attend the meeting?　我真的必须出席会议吗?
　It's necessary for us to net the currant bushes.　我们有必要用网盖上红醋栗树。
　It is necessary for them to decide on which type of fuel is most suitable.　他们必须决定哪一种燃料最合适。

　It is necessary that everyone be there in time.　大家都按时到达那里是必要的。
　It's necessary that young and old people should communicate more with each other.　年轻人和老年人有必要保持更多的联系。

　We consider it necessary that the machine should be oiled regularly.　我们认为机器必须定期加油。
　This has made it necessary for agriculture and industry to develop very quickly.　这就使得工农业必须飞速发展。
　I felt it necessary to speak about our shortcomings.　我觉得有必要谈谈我们的缺点。
　Some students hold it necessary to be able to speak English.　有些学生认为能讲英语是非常必要的。
　The National People's Congress holds one session each year. When necessary, the session may be advanced or postponed.　全国人民代表大会每年召开一次会议，必要时，会期可以提前或推迟。
　If necessary, the heavy machinery can be brought into action.　若有必要，可以使用重型机械。
　If necessary, I'll go there again.　如有必要，我会再去那里的。

 ♣ a necessary evil
　不得不认可的不合意甚至有害的事物　thing that is undesirable and possibly harmful but must be accepted for practical reasons
　Is war a necessary evil in this world?　战争是这个世界上人们不愿见其发生但又无法避免的事吗?
　The loss of jobs is regarded by some as a necessary evil in the fight against inflation.　有些人认为要遏止通货膨胀就难免有人失业。

 ♣ necessary, essential, needful, requisite
　这组词都有“必要的”“必需的”意思。其区别是：
1. necessary为常用词，多指总体上长期而言的需要；needful常指近期或眼下所需；essential含有缺少某一因素便不能运转、生存的意思；requisite常指某一具体任务中所需的具体东西，否则就会影响任务的完成。例如：
　The were the instruments needful for his work.　那是他工作所需要的工具。
　We can live without clothes, but food and drink are essential to life.　没有衣服我们可以生存，但是食物和水是维持生命所必不可少的。
　Past experience is requisite for the job.　过去的经验是做这工作的必要条件。
2. 语气上， essential比necessary强；requisite是正式用语。
3. necessary和essential用在主语从句中时要用“(should+) v."。

　我必须在7点以前完成作业。
　［误］ I am necessary to finish my homework before seven o'clock.
　［正］ It is necessary for me to finish my homework before seven o'clock.
　［析］ 表示“某人必须做某事”时，须用It is necessary for sb to-v结构。

　necessary　偶尔也可用作可数名词，常以复数形式出现，表示“必需品”。例如：
　These are all daily necessaries.　这些都是日用品。

　［同义词］ essential, important, needed, required
　［反义词］ unnecessary
　［词源］　拉丁语necessarius（必需的）