区别辨析though、although与as

though、although与as这些连词均可表示“虽然、尽管”之意。

though和although在意义上几乎毫无区别，但文体上后者是较正式用词，语气比though强。此外，在习惯用法上这两个词仍有以下一些差异：

1. though可引出倒装语序的让步状语从句，although 则不能。
2. though可与even连用，although则不能；在as though结构中，只用though，不能用although。
3. though可以置于从句末，而although则不能。
4. 引出省略句时，通常用though。

• She hasn't called, even though she said she would.
  虽然她说过要打电话，可还没打。
• She walked home by herself, although she knew that it was dangerous.
  她一个人步行回的家，尽管她知道那样做很危险。

as : 引出让步状语从句只用于倒装语序结构中，语气强于上述两个连词。

• Happy as they were, there was something missing.
  尽管他们很快乐，但总缺少点什么。