In a binary statement (either … or …), by affirming one option, it is mistakenly concluded that the other must necessarily be false.
Definition:
The Affirming a Disjunct Fallacy is a formal error in logic stemming from a misunderstanding of the “either … or …” proposition. In this fallacy, the reasoner, by affirming one option, wrongly or deliberately rejects the other. This error typically arises from assuming that the options are mutually exclusive, whereas in reality, both options may be true at the same time. For example:
“Either this writer is talented or prolific. He is prolific. Therefore, he is not talented.”
Here, it should be noted that a writer can be both prolific and talented.
The typical structure of this fallacy:
- Either A or B
- A is true
- Therefore, B is not true
In this structure, since “either” can include both options, the conclusion is invalid.
Examples from real life:
1. In education:
“Either he is intelligent or hardworking. He is intelligent. Therefore, he is not hardworking.”
Here, it should be noted that a person can be both intelligent and hardworking at the same time.
2. In science:
“Either the medicine was effective or the diet was beneficial in the patient’s recovery. The medicine was effective. Therefore, the diet was not beneficial.”
Here, it should be noted that both may have been effective and contributed to the patient’s recovery.
3. In politics:
“Either this government values press freedom or academic freedom. This government values press freedom. Therefore, it does not value academic freedom.”
Here, it should be noted that the government may value both.
4. In everyday life:
“Maria must either do the shopping today or clean the house. She did the shopping today. Therefore, the house was not cleaned.”
Here, it should be noted that she may have been able to do both.
5. In advertising:
“Either this product is the best or that one is. You have chosen this product. Therefore, that one is bad.”
Here, it should be noted that both products may be good.
Why is this fallacy dangerous?
- It creates a false dichotomy: choices are limited to two options, while other possibilities may also exist.
- It leads to simplistic conclusions: it assumes that only one option can be true, whereas both may be true at the same time.
- It eliminates opportunities: in real decision-making, this fallacy can cause valid choices to be overlooked.
- It is a tool for advertising and political manipulation: by forcing people to choose one option, the others are unjustly excluded.
How can we recognise and respond to it?
If you hear an argument based on “either … or …”, ask:
– “Are these two options truly contradictory?”
– “Is it possible that both are true?”
– “Is there any reason why only one of the two could be possible and not the other?”
A suitable response might be: “Your argument is flawed by the Affirming a Disjunct Fallacy. The truth of one option does not necessarily mean the other is false, unless you can prove that the options are mutually exclusive [1].”
Conclusion:
The Affirming a Disjunct Fallacy underscores that we should not assume every “either … or …” statement to be exclusive by default. In reality, it is often possible for more than one option to be true at the same time. Recognising this fallacy helps us avoid falling into false dichotomies and make more informed choices.
[1] By “mutually exclusive” it is meant that the two options cannot both be true at the same time; the truth of one necessarily implies the falsity of the other. For example:
“When a coin is tossed and lands on the ground, either the heads side is visible or the tails side is. If heads is visible, then tails is not; it is impossible to see both at once.”