謂語動(dòng)詞只能做謂語.如：He sat on the bench.sat是謂語
非謂語動(dòng)詞不能做謂語,但是可以擔(dān)任其他成分.如：He was reading,sitting on the bench.sitting就是非謂語.
一般情況下,任何一個(gè)句子都必須有謂語.在具備謂語的前提下,如果還有動(dòng)詞出現(xiàn),你就可以確定把它當(dāng)謂語動(dòng)詞還是非謂語動(dòng)詞使用.如剛才的句子：
He was reading,sitting on the bench.(一個(gè)謂語+一個(gè)非謂語)
可以兩個(gè)謂語動(dòng)詞：He was reading and sitting on the bench.
非謂語動(dòng)詞可以擔(dān)任除謂語以外的任何成分.
限于篇幅,恕不贅言.