Welcome to #FallacyFridays, the day of the week we use to learn all about the flaws in our logic. Today’s logical fallacy is one of my favorites. It’s called Affirming the Consequent. Read on to find out how it works. And test your understanding of it with the quiz at the end. 🤓

The affirming the consequent fallacy makes the mistake of assuming that if a statement is true, then the reverse of that statement is true.

The Affirming the Consequent fallacy follows the “if, then” pattern. It goes a little somethin’ like this:

If A, then B.
It’s B. Therefore, A.

Now let’s apply this pattern (or “syllogism”) to some real-life scenarios.

Example #1 of the Affirming the Consequent Fallacy

“If it’s a dog, then it growls.
It growls. Therefore, it’s a dog.”

Here, A = “it’s a dog” and B = “it growls”

“If it’s a dog (A), then it growls (B).
It growls (B). Therefore, it’s a dog (A).”

Now, you don’t need a Ph.D in zoology to know that this reasoning isn’t necessarily the case. There are animals like tigers, lions, and other wild cats that growl. Dogs aren’t the only ones.

Example #2 of the Fallacy

“I know Paul likes chilis in his soups. It never fails to make him smile. To make him smile, I am going to make chili soup for him. But wait…he came home with the biggest grin on his face today. Obviously, someone else already made chili soup for him and he ate it.”

Now this example isn’t as obvious as the first one. But if we peel back the layers, exposing the bare bones of the rationale here, we can see it’s the affirming the consequent fallacy at play:

If Paul eats chili soup, then he smiles.
He smiled. Therefore, he ate chili soup.

(Here, A = Paul eats chili soup, and B = he smiles/smiled.)

Unless Paul has some type of condition that him only smiling when he eats delicious chili soup, it’s pretty clear why this is reasoning is the affirming the consequent fallacy: Paul can smile because of things other than chili soup.

(If, however, you do discover a condition that has people smiling ONLY because of chili soup, I will gracefully take this L and you best publish your findings and get your Nobel Prize! And give me 40% of the prize money. 👀)

Okay so by now, you probably get how this fallacy works.

But that name though…why is it called “affirming the consequent?” 🤔

Well, let’s look back at the first half of the syllogism I showed you earlier:

“If A, then B.”

A comes before B. That makes A the antecedent. (Fun fact: ante is Latin for “before.”) Since B is the outcome of A, that makes B the consequent.

Now let’s look again at the last half of the syllogism:

“B. Therefore, A.”

Since you’re saying B happened (as seen in this second half of the syllogism) and since it was the consequent (as seen in“If A, then B”), you are…affirming the consequent! 😁

The affirming the consequent fallacy makes the mistake of assuming that if a statement is true, then the inverse of that statement is true. Click To Tweet

Moral of the story: the reverse of true situations are not necessarily true. We can have more than one reason why something occurs.

Quiz time!

And now for the quiz! Below are 4 answer choices. Which one contains the affirming the consequent fallacy?

A. “Cindy loves strawberry starburst candy. It’s the only flavor that she likes. So when she was given an orange starburst, she wasn’t thrilled.”

B. Nonso keeps eating dairy ice cream even though he’s lactose intolerant. Today, he got the dairy free option and his stomach felt much better.

C. Muyiwa hates going in the deep end of the pool, so he wasn’t happy when his siblings tried to convince him to go there. Two days later, he was upset all over again. Ugh, his siblings must be bothering him again.

D. Iris has stage fright. So when he was told to perform for the crowd, he froze.

Which answer choice contains the affirming the consequent fallacy?

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