This type of fallacy occurs when the conclusion does not logically follow from the premises. That is, the reasons are irrelevant to the conclusion. When the premises provided in the argument are not clearly connected to or guarantee the truth of the conclusion. Arguments that have true premises and true conclusions can often be convincing, but be careful! The reasonableness of the reasons or conclusion mean nothing if the reasons are not connected (do not lead) to the conclusion.
Argument Example: Since cars are bad for the environment because they pollute the air, we should not be using airplanes.
Premise 1: Cars are bad for the environment
Premise 2: Cars pollute the air
Conclusion: Airplanes should not be used.
While the premises about cars are true, the conclusion has nothing to do with cars. This argument is illogical because the reasons provided do not clearly support the claim that we should not be using airplanes.