conjunction [从属连词]（表条件）如果；（表假设）要是，假如；无论何时；虽然，即使；（用于间接疑问）是否；（用于礼貌问询）是否；当，每次；（与情态动词连用）表婉转客气；这不是…，要是…多好；或许不；就算；尽管You use if to introduce a subordinate clause in which you admit a fact that you regard as less important than the statement in the main clause.(引导从句，提出次要的事实) 即使
noun [抽象名词]条件，设想；不确定的情况You use if ever with past tenses when you are introducing a description of a person or thing, to emphasize how appropriate it is.(与过去式连用，强调对人或事物的描述极为恰当) 如果有…的话