: 看到公司文件有一个句型用法，突然搞不懂，如下
: A is not B or C…
: 这样到底是
: 1. A不是B或A不是C的话…
: 2. A不是B或A是C的话…
: 3.文法有问题
: 再麻烦各位帮忙解决疑惑 谢谢！


A is not B or C.

若B和C是对等的（都是形容词、都是名词...)
则这个句子会被解读为

A is not (B or C).

例：

The dog is not brown or black.

The food is not healthy or delicious.

I am not detached or remote.

It's not on the table or in the cupboard.

Our main need is not food or money. It is education.


由笛摩根定理，not (B or C) 等价于 (not B) AND (not C)

以下为笛摩根定理的证明
（没兴趣的话可以跳过）

Let x be an arbitrary element of (B U C)',
then x ∈ (B U C)'

→ x not∈ (B U C)

→ x not∈ B and x not∈ C

→x ∈ B' and x ∈ C'

→ x ∈ B' ∩ C'

Therefore, (B U C)' ⊆ B' ∩ C' ……………(i)

Again, let y be an arbitrary element of B' ∩ C',
then y ∈ B' ∩ C'

→ y ∈ B' and y ∈ C'

→ y not∈ B and y not∈ C

→ y not∈ (B U C)

→ y ∈ (B U C)'

Therefore, B' ∩ C' ⊆ (B U C)' ……………(ii)

Combining (i) and (ii), we get (B U C)' = B' ∩ C'

从文氏图上看比较直观
https://i.imgur.com/dNIxVsE.jpg

所以

A is not (B or C).
= A is not B AND A is not C.

再看原本的例子

The dog is not brown or black.
= The dog is not brown AND the dog is not black.

The food is not healthy or delicious.
= The food is not healthy AND the food is not delicious.

I am not detached or remote.
= I am not detached AND I am not remote.

It's not on the table or in the cupboard.
= It's not on the table AND it's not in the cupboard.

Our main need is not food or money.
= Our main need is not food AND our main need is not money.