助動詞

助動詞（、英文簡稱：）是一種可以改變主要動詞意義或時態的一組動詞，在印歐語系語言中非常常見。例如英語中的have、can、will、must等。這些助動詞不能自己單獨使用，必須要與另外一個動詞配合使用才有意義。又助動詞在句子中有其固定的出現位置，例如：在直述句中，助動詞通常會出現在主詞之後，但卻在動詞之前： "You must go home tonight." 這個句子中，you 是主詞，must 是助動詞，go 是動詞。另外與助動詞連用的動詞，必須以動詞原形或分詞形式呈現。

下面是助動詞為現在式和過去式比較:
      現在式         過去式 
      can       →   could
      will      →   would
      may       →   might
      shall     →   should(注:shall=will有未來之意。should通常用於現在式，表應該''之意)
      do/does   →   did
      have/has  →   had

參考文獻 
 
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外部連接

動詞