Inferring that P is true solely because Q is true and it is also true that if P is true, Q is true.
The problem with this type of reasoning is that it ignores the possibility that there are other conditions apart from P that might lead to Q. For example, if there is a traffic jam, a colleague may be late for work. But if we argue from his being late to there being a traffic jam, we are guilty of this fallacy – the colleague may be late due to a faulty alarm clock.
Of course, if we have evidence showing that P is the only or most likely condition that leads to Q, then we can infer that P is likely to be true without committing a fallacy.
Cars break down due to flat tires.
My car broke down.
Therefore, it was due to flat tires.
Unless I give evidence that my car broke down due to a flat tire then it does not follow logically that my tire broke down due to a flat tire. If I affirmed that then I would commit the fallacy of Affirming the consequent based on only the first premise cars break down due to flat tires. Evidence is needed to show that my car broke down due to a flat tire.
Men get hurt from marriage.
John is a man.
Therefore, John got hurt from marriage.
This example is obviously a joke and I’m not even married. Let’s assume that men get hurt from marriage for sake of example if it is a bad marriage. If john is a man and he gets hurt, then If I assert that he got hurt from marriage only based on premise one then I would be affirming the consequent solely without actually evidence. I would need evidence showing that John got hurt from marriage.
Dogs are brown.
I have a dog.
Therefore, my dog is brown.
Last example and the simplest example. Dogs are brown, but not all are brown. I have a dog, but I do not affirm that my dog is brown based only on the fact the dogs can be brown. I would affirm that my dog is brown based on me physically seeing that my dog is actually brown. Even though that my dog is black, I didn’t affirm the consequent only on the fact that dogs are brown.
Affirming the Consequent can be detected if it is contained in this logic form:
If P, then Q.
This is an invalid form because even given that the premises are true; the conclusion doesn’t follow logically. Just because Q happens does not mean it is the cause of P. P is the cause of Q. If my car had a bad engine, then it will break down. This is true statement based on solely Q and the result is P. This is an important fallacy to remember when analyzing conditional statements. For example, If God exists, then miracles are possible. Miracles are only possible if God exists. This fallacy is not to complicating and is easy to spot.
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