but通常作并列连词,连接前后表示转折关系的成分,但该词也可以行使从属连词的功能,引导英语中的三大从句,即名词从句、定语从句和状语从句。but引导定语从句时往往表示否定意义,同时要求主句出现否定词语,从而主句和从句构成双重否定,达到一种语气强调的表达效果。在个别情况下,but并无实际含义,但它的使用仍然可以使语气加重。but引导名词从句和状语从句时,常与that-起使用,在非正式语体中,也可以和what连用。除but that引导的条件状语从句位置灵活之外,其他由but引导的从句一般都位于主句之后。 But usually as a parallel conjunction, before and after connection to express the composition of the transitional relationship, but the word can also exercise the function of subordinate conjunctions to guide the three major clauses in English, namely noun clause, attributive clause and adverbial clause. However, guiding the attributive clause often expresses negative meaning. At the same time, it requires the main clause to appear negative words, so that the main clause and the clause constitute double negatives, achieving an expression effect of tone emphasis. In individual cases, but does not have practical meaning, but its use can still make the tone worse. But when guiding noun clauses and adverbial clauses, they are often used with that-in informal styles, they can also be used with what. In addition to the flexible position of the conditional adverbial clause that is guided by it, other clauses guided by but are generally located after the main sentence.