The necessity of modal logic in rhetorical and argumentative analysis

An acquaintance of mine whose love for mathematics I hold in high regard suggested to me today that modal logic was not necessary for debate, and did not factor into debate. He went so far as to suggest that it wasn't even used in logical debate.

This acquaintance knows a man who is building a computer program wherein which two parties can enter the terms of their argument and the program will hold them logically to said arguments. I, interested and not without experience in these sorts of systems, inquired whether this program took modal and deontic systems of logic into consideration, or rather if it were robust enough to support the use of these types of logic. It was at this point that he denied the utility of modal logic in debates.

Through my work on the development of rule engine software, expert systems and fuzzy logic nets I became intimately familiar with the need for alternative and less-known schools of logic such as modal and deontic logic. Especially in expert systems, or in systems which purport to assist in the analysis of philosophical or theoretical research, which is the specific area in which I presently labor.

A modal logic expression might look like the following:

"If A is true, then it is possible that B is true."

If one were assigned to do all it could to prevent B from becoming true, one would need to determine whether A necessarily leads to B, or whether other presently unseen conditions contribute to the rise of B in the system/argument. One brings modal logic to bear on such cases.

In computer science, this becomes very useful in avoiding unecessary processing. If the negation of A necessarily makes B impossible, then one needn't examine the other preconditions leading to B to know that B is impossible. One may state definitively that B is not true without examining all of its preconditions.

In debate, modal logic is even more useful, so useful that it is nearly ever-present. Recognizing and avoiding the acknowledgement or concession of statements which might possibly contribute to undermining one's own argument by implication is fundamental to debate. Knowing that an assertion necessarily leads to a given conclusion is the subject of modal logic, and is why I pay it such high regard. No system for examining the implications and relationships between systems of theory or assertions of fact can afford to ignore this extremely human mode of thought.

I'm not alone in this belief, either.