The difference between 根本 & 并不

The difference between 根本 & 并不

1. 根本 means "simply"

according to Chinese textbook
you can use 根本 in a positive or negative sentence

positive sentence: 我觉得他根本就是一个白痴。 (I think he's simply just an idiot！)

negative 我根本不懂他在说什么。( I simply just don't understand what he's talking about.)

The two examples above, you can see that "根本“ is focusing on emphasizing the statment which you are trying to express.
First example : 我觉得他根本就是一个白痴。 so 他是一个白痴 (he's an idiot.) is the idea of the sentence, and 根本 is just for
emphasizing the idea.
So you can express the same idea without 根本， just say "我觉得他是一个白痴" (I think he's an idiot!)
You are not changing the meaning without 根本，but the the tone of expressing your idea/thoughts is less strong.


2. 并不 means "actually not" according to textbook

mainly used to deny other people's ideas

ie :
      A : 你工作了十个小时，应该很累吧。（ You worked for 10 hours, you're probably very tired.)
      B:  虽然工作了十个小时，但是我并不累。( Actually I'm not tired, although i worked for 10 hours already)

In this conversation, A is assuming B would be very tired after 10 hours of working, but B isn't tired.
So by saying 并不累 (actually not tired), B clearly states he's not tired also denying A's assumption.


Hope those examples and explanation help!
Sometimes reading more examples help understand Chinese more.
Because there are many things/vocabs in Chinese can't be translated in English.  ：）