Doubt in "If then must" condition

Do the right way

Hi 7Sages,

I have a confusion in representing "if then must" conditions.

Suppose there is a sentence given as :
If N is not selected then T must be selected .

So, is the representation like this?
not N -> T
contrapositive is
not T -> N

If here, N is satisfied then does the rule drops away and does T becomes a floater ?

Since there is a 'must' keyword involved..I am confused.

Please clarify this.
Thank you.

paulmv.benthem

Everything you've written looks correct to me! And, yes, assuming there are no other rules bearing on "T," if "N" is satisfied, "T" becomes a floater.

TexAgAaron

Yes you are correct.

/N->T
/T->N

The "if" signals a sufficient condition and the must signals a necessary condition. Your application of satisfying N in the contrapositive example is spot on too. By satisfying the necessary condition, you make the sufficient (T) a floater.

olepueblo

Looks good. You could substitute “is” for “must be” if that is useful.

Do the right way

Thanks everyone for clarifying the doubt. I understood that 'must' and 'can' could be substituted with 'is' and the same rules follows.