by all means，by no means

这一组词并非同义词，而是具有鲜明对立意义的反义语。它们带有强烈的感情色彩，在文句中起加强语势的作用。

By all means的意思是“一定”、“无论如何”、“用一切手段”。例：

You must bring him here by all means．

你们一定要设法把他带到这里来。

This project must be realized by all means．

这个规划必须要实现。

You should by all means warn him before he leaves for Singapore．

你务必在他去新加坡之前提醒他。

By all means亦可用于回答，表示有礼貌的同意，作“好的”、“当然可以”解。例：

May I have one？—Yes，by all means．

我可以拿一个吗？——当然可以。

By no means的意思是“决不”，相当于not at all。例：

She is by no means bright．

她一点儿也不聪明。

I will by no means consent．

我决不同意。

The first step will take quite a long time and can by no means be accomplished overnight．

第一步的时间是相当地长，决不是一朝一夕所能完成的。

请注意下列三点：

（一）by all means和by no means的 means永远用复数形式，“s”不能丢掉。

（二）by all means与by all manner of means通用；by no means 可与 by no manner of means换用，但后者只作特别强调，远不如前者用得普遍。

（三）by any means的意思是“总之”；by some means （or other）的意思是“用某种方式（或方法）”；不要把它们与by all means或by no means混淆。          

(整理:http://www.com10.cn)