I don't know whether they are not here.
我想他們可能會在這里.
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 乍然看來, 此句不難理解, 似乎是:"我不知道他們是否在這里",
相當于I don't know wherther they are here or not. 實際上,
這個句子并不是表示這個意思, 因為它是個特殊句型,
故不能按照字面去理解和翻譯,其內涵相當于I think that they might be here. 正確的譯文如上.

 為什么我們說這是一個特殊的句型呢?在回答之前, 也讓我們先看兩個句子:
 They are here.
 他們在這里.(肯定形式的陳述句)
 Aren't they here?
 他們不在這里嗎?(近乎肯定的疑問句, 說話人的心目中認為他們在這里,
這樣問, 只是想証實自己的想法無誤.)  

 I don't know whether they are not here就是表示類似語義的一種句型.
 句中的I don't know并不是真正的不知道, 而是表示"沒有十足把握"或"未經証實"的意味,
其后的whether they are not here是近乎肯定的猜測內容, 故全句可譯作:"我想他們可能會在這里".

 "I don't know whether...not"和"I wonder whether ...not"
都是同一種類型的特殊句型,老是用以表示說話人主觀看法或猜測的解釋句(a pattern of interpretation).
 
 現在請讀者將現在一段文章譯成漢語, 要注意whether...not所表達的內涵:
 Dr. Aline Wong, a Singapore Government minister, has made a new pitch for
Hong Kong people to migrate there after announcing that the number of Hongkongers
 who have taken up permanent residence since July 1989 had reached about 4,700. Dr.
Wong said Singapore and Hong Konghad much in common. Both had Dynamic economies
 with modern infrastructures¹.
 Therefore, she wonders whether Hongkongers will not migrate to Singapore.