?復合句是兩個或兩個以上的簡單句組成，每個簡單句都有主謂，句子句子之間由連詞連成；復合句分為並列復合句（也稱並列句）和主從或從屬復合句也稱復雜句）。
如：What were you doing when your mother arrived home?
He said that he was late for school yesterday.
復雜句也稱為從句、主從復合句，由壹個主句和壹個或壹個以上的從句構成，用代詞、副詞、連詞把壹個簡單句作為另外壹個簡單句的從屬成分的句子；某個句子成分直接由從屬分句表示，那麽這種句子便不是簡單句而是復雜句。
如：The students would have made better grades if they had studied hard.
簡單句就是只含有壹個主謂結構並且句子各成分都只由單詞或短語構成的獨立句子或分句。在簡單句中主語和謂語是句子的主幹，是句子的核心。
如：I like English very much.?
?You are a good student.