非谓语动词是指在句子中不做谓语的动词，常见的有四种形式：动名词、to do不定式、现在分词和过去分词。逻辑主语就是非谓语动词所表示的动作的执行者或承受者。
例如：
◆ He admitted taking the money. 他承认(他)拿了那笔钱。
He 是句子主语，admitted 是谓语，taking是非谓语动词，这一动作的发出者是he， 所以非谓语动词taking的逻辑主语就是he, taking the money作宾语。
◆Finishing his work, he went to bed immediately. 完成工作后，他立即上床睡觉了。
非谓语动词finishing的逻辑主语是句子的主语he，finishing his work作时间状语。
◆Feeling tired, I went to bed early. 我感到累，很早就睡了。
现在分词短语feeling tired的意思“感到累了”，作原因状语，动作的发出者是句子的主语I，现在分词语feeling tired的逻辑主语与句子主语一致。
◆Taken in time, the medicine will be quite effective. 及时吃，这药会很有效的。
过去分词短语taken in time的意思是“被按时服用”(注意过去分词含有被动意味)，作条件状语，其逻辑主语是句子的主语the medicine。
如果分词的逻辑主语与句子主语不一致，就可能造成错误。
下面我们来分析下容易掉进“坑”里的句子。一定要仔细哦，没准你也掉进去过呢。比如：
◆Finding her car stolen, a policeman was asked to help.
诊断：句中现在分词短语finding her car stolen的意思是“发现车被盗”，发现车被盗的主语当然是“她”，所以句子的主语应用she，而不应该用a policeman。
改正：Finding her car stolen, she hurried to a policeman for help.
◆In order to attract visitors, historic buildings should be maintained.
诊断：历史建筑是没有生命的，不可能有某种目的(in order to do sth)，真正的逻辑主语应该是人。
改正：In order to attract visitors, city councils should maintain historic buildings.
◆By setting rules, children can reduce behavioral problems.
诊断：setting rules的主语不是children，应该是学校。
改正：By setting rules, schools can reduce behavioral problems.
◆Compared with Japan, the crime rate in the US was high.
诊断：过去分词compared的主语应该是the US，而不是the crime rate。
改正：Compared with Japan, the US had a higher crime rate.
事实上完整的句子是：When the US is compared with Japan, the US had a higher crime rate.
◆Many companies have required employees to work overtime, performing all tasks before going home.
诊断：主句的主语是many companies, 而performing的主语应该employees, 所以应该要把主语改成employees。
改正：Employees are required to work overtime in many companies, performing all tasks before going home.
非谓语动词是高中语法中的重难点，在短文阅读的句子中会频繁出现，非谓语动词掌握得不好，就看不懂文章，阅读理解难拿高分。