Is there a single noun that describes "need not"?

There are four types of deontic modality, which can be expressed by the following modal expressions:

1. Can
2. Need not
3. Must not
4. Must

Out of these, 1, 3, and 4 respectively corresponds to the following nouns:

1. Permission
2. ???
3. Prohibition
4. Obligation

Is there a simple word that corresponds to type 2?

Solution 1:

Remission has a sense of exemption from doing something. So either of the two could serve the purpose.

Solution 2:

Optionality - noun form for the quality of being Left to choice; not compulsory or automatic.

Apparently this word has become significantly more common over the past 50 years.

Solution 3:

Unnecessity would fit the bill, if only it weren't obsolete. However, needlessness is not obsolete. To avoid the contrived aura, you may desire to go for a longer phrase and just use absence of necessity or lack of necessity. Or, consider using a positive-oriented word: optionality.

I gave FumbleFingers an upvote on optionality and wanted to point out that it is not only significantly more common than it was fifty years ago, it has even become more common than any of the other options:

On that basis, I think optionality deserves the cake on this issue.

Solution 4:

When need is used in the positive form it signifies necessity. In the negative form it signifies lack of necessity.

Solution 5:

What about elective?

Elective: not compulsory; optional ; possible but not necessary; left to personal choice

You need to take this course = You are required to take this course (required course)

You needn't take this course = This course is elective to you (elective course)