状语从句知识点总结：unless与if…not表示否定条件时有何区别
<p>【导语】英语语法让很多学生都头疼，因为复杂难懂的句式和词组有时难以记忆。英语网为大家整理了英语语法大全，希望对同学们的英语语法学习有所帮助。更多内容尽在英语网。</p><p>两者都可表示否定的条件，有时可换用。如：</p><p><span word="Come">Come</span> <span word="tomorrow">tomorrow</span> <span word="unless">unless</span> <span word="I">I</span> <span word="phone">phone</span> [<span word="if">if</span> <span word="I">I</span> <span word="dont">dont</span> <span word="phone">phone</span>]. 要是我没有打电话，明天就来。</p><p><span word="You">You</span> <span word="wont">wont</span> <span word="catch">catch</span> <span word="the">the</span> <span word="train">train</span> <span word="unless">unless</span> <span word="you">you</span> <span word="hurry">hurry</span> [<span word="if">if</span> <span word="you">you</span> <span word="dont">dont</span> <span word="hurry">hurry</span>]. 你要是不赶快，你就赶不上火车了。</p><p>但是在下列情况下，通常要用 <span word="if">if</span> ... <span word="not">not</span> 而不用 <span word="unless">unless</span>：</p><p>1. 当从句所引出的情况不是表示主句情况发生的一种例外而只是一种可能，并且这种可能正是导致主句情况发生的主要原因时，英语习惯只用<span word="if">if</span>...<span word="not">not</span>，不用<span word="unless">unless</span>。如：</p><p><span word="Ill">Ill</span> <span word="be">be</span> <span word="surprised">surprised</span> <span word="if">if</span> <span word="he">he</span> <span word="doesnt">doesnt</span> <span word="win">win</span>. 如果他不赢，我会感到惊奇。</p><p><span word="Shed">Shed</span> <span word="look">look</span> <span word="nicer">nicer</span> <span word="if">if</span> <span word="she">she</span> <span word="didnt">didnt</span> <span word="wear">wear</span> <span word="so">so</span> <span word="much">much</span> <span word="make">make</span>-<span word="up">up</span>. 要是她不过分打扮，本来会更好看的。</p><p><span word="Ill">Ill</span> <span word="be">be</span> <span word="sorry">sorry</span> <span word="if">if</span> <span word="they">they</span> <span word="do">do</span> <span word="not">not</span> <span word="come">come</span> <span word="tomorrow">tomorrow</span>. 如果他们明天不来，我将感到非常遗憾。</p><p>2. 当从句内容与已知事实相反时(即引出虚拟条件时)，通常要用<span word="if">if</span>...<span word="not">not</span>，而不用<span word="unless">unless</span>。如：</p><p><span word="If">If</span> <span word="he">he</span> <span word="werent">werent</span> <span word="so">so</span> <span word="silly">silly</span>, <span word="he">he</span> <span word="would">would</span> <span word="understand">understand</span>. 他要不是那样傻的话，他就会明白了。(实际上他很傻)</p>
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