1) 一般词典的解释是 at all 加强否定或疑问或准否定的语气，这个意义比较容易掌握。

• They don't like him at all.他们一点也不喜欢他。
• Do you know him at all?你到底认不认识他？
• Are you even police officers at all?你们还算是警官吗？
• Has he tried to contact you at all?他到底有没有同你联系过？
• Come late? He didn't come at all.来晚了？他根本就没来。
• It (prostate cancer) is a cancer that doctors debate not just how to treat but whether they should treat at all. 前列腺癌是一种医生们不但争论如何治疗而且还争论根本该不该治疗的癌症。
• He couldn't help wondering how anybody ever walked out of there with any money left in their pocket at all.他不能不琢磨怎会有人能够离开时兜里还有钱剩下来。

if 从句也有怀疑不定的意义，所以里面的 at all 可以加重“即使”、“万一”的不肯定语气。

• They'll come late, if they come at all.他们就是来也会来晚的。
• Seldom if at all.即使有也很罕见。
• If you do it at all, do it well.不做则已，一做就好好做。
• Medical care was not free for them, if they could get it at all.他们即使得到医疗照顾，也不是免费的。
• I can see only with great difficulty, if at all.我即使看得见，也十分吃力。

如果主句有表示惊讶的意思，从句（引起惊讶的事实）也可以用 at all 来加重“竟然”的语气。

• It would surprise me, if he had seen that guy at all.如果他竟然见过那个人，我就会很惊讶。
• It was truly a miracle that he survived at all.他活了下来，的确是个奇迹。

2) 但是在肯定句中，at all 的意义就比较微妙。大体上，有“究竟”、“到底”、“总算”、“终于”甚至认为不大可能或不应该发生的事竟然发生的“竟然”、“即使”或“万一”的意思。

• How this pair of vases managed to survive at all is still another mystery.这一对花瓶是如何竟然保存下来的，这又是一个谜。
• My original question, why he did it at all, has not been answered.我原先的问题，他到底为什么这样做，还没有得到答案。
• Patroni himself had remembered several times, with concern, his reason for being out at all tonight... (Arthur Hailey, Airport, p.44)帕特罗尼自己已经好几次忧心忡忡地记起他自己今天晚上到底是为什么出来的…
• With the grazing wound the bullet had caused to his head, it was a wonder he had regained consciousness at all, but he had.子弹擦伤了他的头部，他却竟然能够恢复知觉，简直是个奇迹，但他还是恢复了。
• They scoffed that he should be charged at all.对于他竟然被指控一事，他们采取嘲笑态度。
• That such an assessment should be made at all was in itself paradoxical.竟然作出了这样一个评估，这件事本身就很奇怪。
• The faculty for myth is innate in the human race. It seizes with avidity upon any incidents, surprising or mysterious, in the career of those who have at all distinguished themselves from their fellows, and invents a legend to which it then attaches a fanatical belief. (Somerset Maugham, The Moon and Sixpence, Chapter I)制造神话是人类的天性。对那些毕竟与众不同的人物，如果他们生活中有什么令人感到诧异或者迷惑不解的事件，人们就会如饥似渴地抓住不放，编造出种种神话，而且深信不疑，近乎狂热。

与 any 连用时，at all 突出了“任何”这个意义。

• I'll do any job at all—even road-sweeping.我什么活都干，哪怕是扫大街。

与 only 和 any 连用时，at all 有“总算是”的意思。

• Of the twenty projects under construction, only seven had been completed and were producing anything at all.二十个建设项目中，只有七个已经完工，总算是生产出点东西。

在连续列举几件事情的最后，来一个总概括，说到底，囊括一切，也可以用 at all。

• However, Ernestina did her best to be angry with her (= Aunt Tranter); on the impossibility of having dinner at five; on the subject of the funereal furniture that choked the other rooms; on the subject of her aunt's oversolicitude for her fair name... and above all on the subject of Ernestina's being in Lyme at all.(John Fowles, The French Lieutenant's Woman, Chapter 5)谁知，欧内斯蒂娜却偏偏跟姨妈处处做对。她对五点钟不能准时开晚饭感到不满；对塞在其他房间里的那些单调的家具不满；对姨妈过分关心她的名声不满…欧内斯蒂娜感到最不满的是，她觉得自己本来就不应该到莱姆镇来。