句子中间部分将介词短语所做的伴随状语前置,做了插入语,形成分隔结构.
正常语序：
I went to school and bought a crips without saying a word.
或
Without saying a word, I went to school and bought a crips.
插入语不能是任何词语或句子,要看它在句子中的成份,只有非主要成份（定语、状语、表语、补语、同位语）能做插入语,原因是由于这些成分在句中仅起到补充说明作用,改变其在句中的位置不会影响句子逻辑结构,因此对于它们在句中的位置并没有严格要求,故可作为插入语前置或后置.
例句：
Jack, a friend of mine, is a good person. 同位语做插入语
Few people, however, can criticise this situation in perspective. 让步状语做插入语