2021年12月英语六级第3套真题句子解析： Leo Tolstoy was even bolder: "The most difficult subjects can be explained to the most slow-witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of a doubt, what is laid before him."

if he has not formed any idea of them already

第一分句"The most difficult subjects can be explained to the most slow-witted man"是主句，其后跟条件状语从句"if he has not formed any idea of them already"（第一层嵌套）。在同一主句结构中还有"can be explained"的被动结构。虽有两层，但结构较为简单直接。

but the simplest thing cannot be made clear

冒号后的内容由两个独立主谓结构组成：第一分句"The most difficult subjects can be explained to the most slow-witted man if..."，第二分句"the simplest thing cannot be made clear to the most intelligent man if..."，两者由对等连词"but"连接，构成转折关系的并列句。前者说困难的主题可以讲给理解慢的人，后者说简单的事情却讲不清给固执己见的聪明人，形成鲜明对比。

if he is firmly persuaded that he knows already, without a shadow of a doubt, what is laid before him

主句"the simplest thing cannot be made clear to the most intelligent man"（第0层），后接条件状语从句"if he is firmly persuaded that..."（第一层），该条件从句中嵌套宾语从句"that he knows already...what is laid before him"（第二层），而这个宾语从句中"what is laid before him"本身又是一个宾语从句（第三层）。这是典型的三层嵌套结构，从句层层包含，构成理解难点。

he knows already, without a shadow of a doubt, what is laid before him

动词"knows"的宾语从句"what is laid before him"本应紧随其后，但被插入语"without a shadow of a doubt"和副词"already"分隔开。这种分隔使得"knows"和它的宾语"what is laid before him"不相邻，需要跳过中间成分才能找到完整的动宾关系，构成理解障碍。

without a shadow of a doubt

在"that he knows already, without a shadow of a doubt, what is laid before him"中，介词短语"without a shadow of a doubt"（毫无疑问）由逗号前后分隔，插入在"knows already"和"what is laid before him"之间，起强调作用，可以去除而不影响句子主干结构的完整性。这是典型的插入语结构。

not formed any idea of them alreadybut the simplest thing cannot be made clear

not...but 结构的核心是「否定前项，肯定后项」的取舍对比框架。识别此结构需把握三个要点：

1. 对等并列：not 和 but 连接的成分必须是同类句法单位。本句中，not 引导的是条件状语从句 "if he has not formed any idea"，but 引导的是独立分句 "but the simplest thing cannot be made clear"，两者在句法层级上都是完整的分句结构，构成对等的对比关系。

2. 取舍语义：not 否定的情况（「没有预设观念的迟钝者」可以理解难题）与 but 肯定的情况（「有坚定成见的聪明人」无法理解简单事物）形成鲜明的逻辑对比，体现「并非A的情况，而是B的情况」的取舍关系。

3. 语义重心：but 后的内容是作者真正想强调的观点。托尔斯泰通过这个对比结构，将重心放在「成见阻碍理解」这一更重要的洞察上，not 部分只是铺垫。

实战中需警惕的假阳性：若 not 和 but 分属不同句法层次（如一个在主句、一个在从句内部），或 but 仅表示普通转折而非取舍对比（如 "He didn't study, but he passed" 只是两个独立事实的转折），则不属于此结构。判断标准是：去掉 not 部分后，but 部分是否仍能独立表达完整且对立的观点。