Modus Tollen

Modus tollens are centered around the formula not unlike that of the modus pollen:
If p, then q
not q
Therefore, not p
In other words, if the premise "p" is true, then the premise "q" is also true. However, if "q" is false, then "p" must be false.

For example,
If Emily is buff she will make the football team.
Emily is not buff.
Therefore, she will not make the football team.

We can prove that this statement follows the formula because If "Emily is buff"(p) she will make the football team(q). Emily is not buff(q). Therefore, she will not make the football team(p).