what名词性从句和whatever名词性从句区别

1whatever可用作连接词或连接副词，引导让步状语从句，表示“无论，不管”的意思。此时，可用no matter what结构来替换其意完全相同。位置前后置都可以。
2whatever还可以引导名词性从句，同时起先行词和关系代词的作用。相当于anything that或all that，有任何一切这类意思。此时不能用no matter what替换。
3what和ever分开写，则作“到底，究竟”解，这时它和on earth, in the world相同，起强调作用。e.g. What ever do you mean? = What do you mean on earth?
4what也可以引导名词性从句意为“the thing which”与“whatever”含义相同。
5用法完全与whatever相同的词还有whichever,whoever.

what 在名词性从句中的用法相当于the+ 名词 +that/which
whatever=anything+that
you can take whatever/what you like.
what we need is time.(what=the thing)
what we call USA today is a powerful country.(what=the country)

从中文语义上理解，whatever是无论哪个，你把意思代进去读一读，用中文翻译一下，通了就是了。
这是最简单的办法。