虚拟语气指的是当一个人说话时欲强调其所说的话是基于自己的主观想法，愿望，假想，猜测，怀疑或建议，而不是根据客观实际，就用虚拟语气。GMAT语法考试只考陈述语气和虚拟语气，而虚拟语气又是考试中的难点，所以本文给大家介绍的就是GMAT语法时态语气试题讲解之虚拟语气。由于文章内容很多，所以我们分为三部分给大家介绍，本文是第一部分。
例1：
Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, until almost 1900, scholars and critics did not begin seriously to study traditional Native American poetry in native languages.
A until almost 1900, scholars and critics did not begin seriously to study
B until almost 1900 scholars and critics had not begun seriously studying
C not until almost 1900 were scholars and critics to begin seriously to study
D it was not almost until 1900 when scholars and critics began to seriously study
E it was not until almost 1900 that scholars and critics seriously began studying
分析：未划线部分有个Although，它所在的句子当中的主语带了一个表示时间的美国诗人，这个时间不能当做时间状语，只能算作定语，句子时态用了had professed，后边还并列了一个谓语had pretended ，所以句子时态是过去完成时，如果句子当中出现了过去完成时，那么一定要有一个过去时态的谓语动词，因为这样才能体现谓语动词的先后动作，接下来是划线部分，可以看到划线部分的确是用的过去时态，但是它的时间状语是待定的，原因在于until almost 的后面的时间状语，前后都有逗号，既然前后都有逗号，那么既可以修饰Although引导的让步状语从句，也可以修饰后面句子的主语，所以只有until 修饰的是主句的谓语动词的时候，主句才能用过去时态，所以A选项排除。
B选项，时间状语没有问题，但是谓语动词用的是过去完成时，有问题，所以B选项排除。
C选项，not until 在句首，我们知道否定词在句首，句子的谓语动词是要用倒装的，这里倒装没问题，但是多加了一个be to do 的形式，begin to 本来就是主动地表达，用在这里不仅是主观而且是倒装，另外seriously作为副词不能修饰名词和代词，但是动词和介词短语都可以修饰，所以这里seriously既可以修饰begin也可以修饰to study，排除C.
D选项，时态没问题，但是句意完全改变了。因为Although引导的让步状语从句的主句当中说到了直到20世纪，那么很明显，根据这个句意它想说的是，直到20世纪的时候，这些学者才开始认真的钻研，所以才会有Although引导的让步状语从句当中说这些诗人，在什么时候是对它感兴趣的。这样的话就把主句当中的主要成分变成了when引导的状语从句，所以排除D。
正确答案是E.
正确句子：
Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, it was not until almost 1900 that scholars and critics seriously began studying traditional Native American poetry in native languages.
验证：Although引导的让步状语从句是没问题的，而且并列了两个过去完成时态，had professed and had pretended ,主句当中用的是it was…that …的强调句型，很明显这里seriously 修饰的是began这个谓语动词，所以E选项经过验证是没有问题的。
例2：To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
A have to know a great deal more than now about the social and economic
B have to know a great deal more than they do now about the social and economical
C would have to know a great deal more than they do now about the social and economical
D would have to know a great deal more than they do now about the social and economic
E would have to know a great deal more than now about the social and economical
分析：
一开始就有一个 to do 结构，在修饰的时候会发现，to do,doing ,介词+doing以及动词的ed分词形式放在句首，其逻辑主语都是后面句子的主语，所以develop的主语就是后面句子的主语 demographers，接下来往后看，画线句子中出现了一个比较对象now,所以想要和现在比较，那么要不就是过去要不就是未来，我们来看一下句子意思，为了能够得出更加精确的人口统计信息，人口统计学家应该比我们知道更多的现在的信息，想一下，肯定是人口统计学家掌握的信息没有想象当中多，所以应该是一种虚拟的假想，选项A和B用的是一般现在时，陈述的是事实不是虚拟，所以排除，而且A选项对比的对象是时间而不是已经知道的信息和应该知道的信息，所以也不合适，C选项中economical 的意思是经济实惠，不是经济的，排除C。剩下DE两个选项，E 选项对比的是时间状语，D选项对比的是已经知道的信息和应该知道的信息(hey do )，所以排除E.答案是D。
正确句子：
To develop more accurate population forecasts, demographers would have to know a great deal more than they do now about the social and economic determinants of fertility.
验证：to do表示目的，demographers是句子主语，would have to know是谓语动词，would 是个情态助动词，在这里表示虚拟，指的是现实中没有知道这么多信息，所以do实际上指的是know.
》》点击了解GMAT语法时态语气试题讲解之虚拟语气（二）
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