Comma before "not"

If I have this opposition construction with not like

It's all about intimidation(,) not the law.

should I place a comma before not?

Solution 1:

Yes you should.

It's all about intimidation (pause) not the law.

The pause is provided by the comma. Another reason might be that this could be thought of joining to different sentences.

It's all about intimidation. It is not about the law.

Solution 2:

Someone should note that the above advice about putting a comma where you "hear it" or "take a breath" is only (if that) applicable to non-American English. In American English, there are rules to when you do and do not use commas, and they are not based on hearing, breaths or pauses (although certainly there is some overlap). The above comma usage is correct because "not the law" is a dependent clause.