应对SAT考试的语法部分，重要的策略就是分类整理、理清吃透，将各类语法结构在脑中形成一种固定模式。下面澎博英语的老师们给大家讲解一下SAT语法独立主格结构，供大家参考。

首先同学们得明确独立主格结构的概念：

1. 由名词或代词加上分词等构成的一种独立结构，用于修饰整个句子。

2. 需特别注意的是，独立主格结构与主句之间不能使用任何连接词。

3. 这种结构与主句不发生句法上的联系，它的位置相当灵活，可置于主句前、主句末或主句中，常由逗号将其与主句分开。

4. 独立主格结构中的名词或代词与其后的分词等构成逻辑上的主谓关系。

而独立主格的构成形式可能是名词(代词)+现在分词(过去分词;形容词;副词;不定式;名词;介词短语);或者是with，without 引导的独立主格结构;它的句法功能则一般是作状语，表示时间、条件、原因、伴随状况，补充说明等，还可以作定语。

看一些SAT考过的历年真题：

1. 2009.5/ S10.10 独立主格作伴随状态(名词+ing) 

  A thick growth of sunflowers standing ten feet tall, their brown heads drooped over the fence with the weight of their seeds.

(A) standing ten feet tall, their brown heads drooped

(B) standing ten feet tall, their brown heads drooping

(C) standing ten feet tall, and their brown heads droop

(D) stood ten feet tall, their brown heads drooping

(E) stood ten feet tall, and their brown heads drooping

很多同学认为A选项没有错误，认为名词sunflowers+现在分词ing分词构成的独立主格成分相当正确，主句也有主谓brown heads drooped, 从而不假思索地选择A选项。但这样思考的同学其实忽略了独立主格结构的本质，即它一般表示主句后的伴随状态，补充说明。也就是它应该属于次要的成分，原句中的代词their暗示了brown heads drooped应属于伴随状态。因此，A选项犯了“主次不分”的错误。我们纵观选项，正确答案应为D。当然其余选项一眼便知其错误之处，B选项的整个句子缺少动词，而C和E则犯了同样的错误，即在独立主格和主句之间用了连词。

2. 2012.1/S6.11 独立主格作补充说明 (名词+ed)

  The island of Madagascar, off the coast of Africa, is the habitat of more than 200,000 species of plants and animals, many are not found anywhere else on the planet.

(A) animals, many are not found anywhere

(B) animals; many, not found anywhere

(C) animals; of which many are not found anywhere

(D) animals, many found nowhere

(E) animals, finding many nowhere

根据语法的基本原则：逗号不连接两个句子，而分号可以连接——我们可以轻易排除A, B, C选项。同学们容易误选E选项，错以为D选项的后半句也是一句完整的句子，因而违背组句基本原则。此刻不要忘了，“名词+过去分词”也是独立主格结构的特征(表示受动)，例如He was listening attentively in class, his eyes fixed on the blackboard. (他上课专心听讲，眼睛紧盯着黑板。)其实D选项完全正确，而E的finding动作的逻辑主语并不是island,而是动植物，因此不对。

3. OC Test 5 S10 14 (名词+to do)

Bats and mosquitoes come out at twilight, and the bats would look for mosquitoes and the mosquitoes would look for people.

(A) and the bats would look for mosquitoes and the mosquitoes would look

(B) and the bats come to look for mosquitoes while the mosquitoes look

(C) the bats look for mosquitoes and the mosquitoes are looking

(D) the bats looking for mosquitoes while mosquitoes would look

(E) the bats to look for mosquitoes and the mosquitoes to look

此题根据连词前后乍一看, 大家会从平行结构之对称原则来做判断, 发现B, C, D三个选项皆存在时态紊乱不对称,结构复杂的问题, E 选项，用了“名词+ 不定式”构成独立主格，而且对称平行，要优于A选项的繁琐句式。因此正确答案是E。

4. 2012.1/S6.9 独立主格作原因状语( 名词+ing)

An odd friendship in certain respects, she being an outdoor enthusiast and he a dedicated bookworm.

(A) An odd friendship

(B) As an odd friendship

(C) Their friendship being odd

(D) Theirs was an odd friendship

(E) Having a friendship that was somewhat odd

有部分SAT语法教师都会在上课时指出having和being在句子中表时态是“自杀词”。的确，基于“句子必须有主谓”，“选项要尽量简洁”的基本原则，利用“自杀词”可以迅速排除选项。但有些同学在学习过程中容易太片面，知其然，而不知其所以然。因此，粗心大意者遇到此题的时候甚至会觉得不知所措。而细心者则会注意到后半句(she being an outdoor enthusiast and he a dedicated bookworm)其实是独立主格结构(名词加ING分词)表示原因。 那么句子的前半部分必然是主句，必须有主谓，因此符合的只有D选项。

最后，我们在ISE中综合地看一下吧。

 A gray owl flying low 

(A) across a forest clearing, its wings beating

(B) quietly and its ultra-sensitive ears turned to the faint sounds

(C) made by small creatures concealed

(D) under leaves. No error

(E) (09-5-S4-24)

好多同学深受这题的困扰，问题就在于整个句子的主要动词到底哪个，是fly, beat, 还是turned 呢?也有同学根据平行结构，即刻判断B选项beating错误，因为它与and 后面的turned不平行。如果这样的话，整个句子便犯了我们最初讲述的“主次不分”的错误(第一题)。its wings beating quietly and its ultra-sensitive ears turned to the faint sounds 由代词带起，综合了名词+ing(施动), 与名词+ed(受动) ，表示伴随状态，构成两个独立主格，而主句主语是a gray owl,却缺少动词，因此选项为A (flying low)。

以上就是SAT语法独立主格结构的讲解。希望同学们对独立主格结构有一个清晰的认识，在遇到这类语法题时，能够得心应手。