句子是表達(dá)完整意義的結(jié)構(gòu)形式，它有獨(dú)立的結(jié)構(gòu)，而不依附于其他成分，除非有特別的語境。一個完整的英語句子通常必須具備兩個基本條件：
(1)表示一個完整的意思
(2)至少包括主語和謂語兩個部分(祈使句除外)
如果將句子的某一部分(短語或從句)當(dāng)作一個完整的句子，如將從句、同位語、短語當(dāng)作句子，或者將現(xiàn)在分詞、過去分詞、動名詞、不定式當(dāng)作謂語，或者句中缺少主語或謂語就會導(dǎo)致非完整句。試比較：
不完整：While they always try to avoid the number of 4 for its connection with death in pronunciation.
完整：However,they always try to avoid the number of 4 for its connection with death in pronunciation.
不完整：How to write a composition.
完整：How to write a composition is not an easy thing to talk about.
不完整：If the weather were fine.
完整：If it were fine,we would have a good time.
(1)表示一個完整的意思
(2)至少包括主語和謂語兩個部分(祈使句除外)
如果將句子的某一部分(短語或從句)當(dāng)作一個完整的句子，如將從句、同位語、短語當(dāng)作句子，或者將現(xiàn)在分詞、過去分詞、動名詞、不定式當(dāng)作謂語，或者句中缺少主語或謂語就會導(dǎo)致非完整句。試比較：
不完整：While they always try to avoid the number of 4 for its connection with death in pronunciation.
完整：However,they always try to avoid the number of 4 for its connection with death in pronunciation.
不完整：How to write a composition.
完整：How to write a composition is not an easy thing to talk about.
不完整：If the weather were fine.
完整：If it were fine,we would have a good time.