If P, then Q. It is not the case that P. Therefore, it is not
the case that Q.
The symbolic form looks like this;
If it is raining, then it is cloudy. It is not raining.
Therefore, it is not cloudy.
The antecedent's presence guarantees the consequent's presence.
But the absence of the antecedent does not tell us anything about
the consequent. Remember that rain is sufficient to guarantee clouds.
But the absence of rain doesn't mean that there are no clouds.
We can see that the premises of this type of argument do not lead
with certainty to the conclusion. Therefore, the form is a fallacy.