英语短语“be not so much as” 实际上是“be not so much A as B” 结构的简化表述（完整结构必须包含对比的双方“A”和“B”），而单独的“not so much as” 也有独立用法。以下是详细解析：
A和B需为同类语法成分（名词、形容词、介词短语、从句等），用于对比两种属性或特征。
“be”动词随主语变化（am/is/are/was/were等）。
He is not so much a teacher as a mentor.（与其说他是老师，不如说他是导师。）
This is not so much a mistake as a deliberate choice.（这与其说是错误，不如说是故意的选择。）
The movie is not so much funny as heartwarming.（这部电影与其说搞笑，不如说暖心。）
She was not so much angry as disappointed.（她与其说生气，不如说失望。）
His success is not so much due to talent as to hard work.（他的成功与其说靠天赋，不如说靠努力。）
The decision was not so much based on logic as on emotion.（这个决定与其说基于逻辑，不如说基于情感。）
当“not so much as”不接对比的B时，单独表示“甚至不；连…都不”（= not even），强调程度之低或出乎意料。此时句子谓语通常为否定的实义动词（如didn’t, couldn’t等），而非be动词。
例句：He didn’t so much as say “thank you” after I helped him.（我帮了他后，他连“谢谢”都没说。）
She couldn’t so much as lift the box—she was too weak.（她连箱子都提不动——太虚弱了。）
I haven’t so much as seen him in a year.（我一年来连他的面都没见过。）
be not so much A as B：对比关系（强调“更倾向于B”）；
not so much as（独立用）：强调否定的程度（“甚至不”）。
若见到“be not so much as”，需补全对比的A和B（完整结构是“be not so much A as B”）；
若“not so much as”单独用，意为“甚至不”，修饰实义动词的否定。
通过例子记忆更清晰，建议结合语境理解！