必须: must/ have to 必需: need

我们举两个例子：你必须去学校。 水是我们生活必需品。 第一句：必须表示：一定要...... 第二句：重点（key)在“需”表示：需要，通常和“品”连用，表示不能缺少。 你可以自己在用这两个词造句。

“必须” is an adverb, usually used to modify a word or phrase which can be regarded as a verb as a whole. E.g. 你必须停止玩游戏。 Here 停止 and 玩游戏 are a verb and a phase which can be regarded as a verb respectively. And 必须 therefore has been used. "必需" is an verb, usually used to modify a word or phrase which can be regarded as a none as a whole. E.g. 房间中只有一些日常生活必需用品。 Here 用品 is a none and therefore 必需 has been used. You could also refer to other examples in this page that have been taken by other italki users. Rules hold for these examples as well. Apart from these, pls notice there is an special case that “必需”, "所" and "的" can be used together as a combining form, that is, "所必需的". E.g. 这些软件是我们发展业务所必需的。 This sentence of example means these software is required for our business development. Ref. http://book.sina.com.cn/nzt/ele/wangyouwenzi/19.shtml ------------------------------------------------ I don't know whether this explanation make sense. If some confusing points still remain, just feel free to let me know.

“必需”与“必须”，音同而形、意不同，使用时常常混淆，实有辨别的必要。 从词意看，“必需”是“一定得有”，不可缺少的。如：衣、食、住是人们生活所必需；煤铁等是发展工业所必需的原料。“必须”是表示事理上和情理上的必要，“一定得要”，如：“学习必须刻苦钻研”。还可用于加强命令语气，如：“明天你必须来。” 从词性看，“必需”是动词，在句子中主要与别的词结合做定语；“必须”是助动词，在句子中只做状语，如：决定了的事就必须做到。另外，“必需”可与其他词合为一个新的词，如“必需品”；“必须”则没有这种构词能力。 http://zhidao.baidu.com/question/3413432.html 必需 is an adj 必需品 its like the word "necessary" in english. 空气对于人来说是必需的。 the air for people is necessary. 必需 is a verb. in english, it is must , it is NOT (have to in chinese have to means 不得不) 你必须去工作 you must go to work ================================ 必须: must/ have to 必需: need ================================ this is totally wrong

必须 是 you have to， must 必需，必需品 is something you really need, you can't .... without it