Question

if,unless引导的从句,放在句首和句尾在用法上有什么不一样

Answer 1

这两个词放在句首或句尾在用法上是一样的, 只是族在句首,就是两个句子, 放在句中,就是一个句子, 也就是说是用if或unless将两个句子连接成一个句子.
例: If it were not for your help, I would not have succeeded.要不是你的帮忙, 我是不会成功的.
= I would not have succeeded if it were not for your help.

unless = if....not用来引导否定的条件句, 也就是说用来代替否定的if从句.
例: If Max doesn't come on time, we will leave without him.如果Max没准时来,我们就不等他先走.
=Unless Max comes on time, we will leave without him.

not+unless=only...if 表示"如果...的话"
例: Venus won't come unless Nancy does. Venus不会来,除非Nancy有来.
=Venus will not oonly come if Nancy does.
注意, 这里的only只是用来强调if , 与 if only(要是...就好了) 意思不同喔~

Answer 2

其实if是可以放在句尾，句首，句中意思一样的！不管怎么变法都是一样的，若这件是是必然发生的，那么if后面，或前面都是一般现在时！UNLESS是“除非”的意思~！