To use "not" or "don't" in a noun clause?

As in this sentence: "We ask that you not take anything you read here as final.", why "not" is used instead of "don't"?

Solution 1:

This is an example of the mandative subjunctive, which is a clause following a mandative word (expressing a demand, requirement, request, recommendation, insistence or suggestion) and usually, but not always, begins with 'that' and contains a bare infinitive.

The bare infinitive can be hard to spot. With inflected verbs such as be, it's easy, as the inflected forms are 'am, are, is', whereas the bare form is 'be'.

I suggest that you be careful.

The important word is the mandative word.

We demand that he return the item immediately.
He insists that Jones go first.

Your example (the mandative word is request or ask):

We ask that you not take anything you read here as final.

is simply a negative mandate. The bare infinitive is take. The negative is not take.

If it were not the subjunctive, do not/don't would be fine. It might read:

Please don't take anything you read here as final. (not a mandate)

Examples of other negative mandative subjunctives:

• We ask that you not bring pets into the area.
• The Park Service requests that you not hike this trail in the event of storms.
• We request that you not send private information to us by email...
• We ask that you not eat or drink for 12 hours prior to surgery...