系动词属于
表语动词，也就是说出现了系动词，这个句型就是主+系+表结构了。而由谓语动词（又称实义动词）构成的句子则是主+谓+宾结构。比较大的区别是，当系动词是be动词（be动词时系动词的一类）时，变否定/疑问句时不需
助动词；而当动词是谓语动词是变否定/疑问句则需要助动词。例如He is a student. He isn't a student. Is he a student?He likes sports. He doens't like sports. Does he like sports?