Mastering Al-Tanaqud: The Rules of Logical Contradiction

The Law of Contradiction: How to Disprove Any Statement

Have you ever been in an argument where both sides claim to be right, but their statements completely clash? In our previous post on the Four Propositions, we learned how to categorize statements. Today, we learn the rules of Al-Tanaqud (Contradiction)—the study of how two statements relate when one must be true and the other must be false.

What is Al-Tanaqud?

In Ilm al-Mantiq, contradiction is defined as a difference between two propositions such that, by their very nature, one must be True and the other must be False. They cannot both be true, and they cannot both be false.

To find the true "contradictory" of a statement, you cannot just change one word. You must follow specific rules regarding Quality (Affirmative/Negative) and Quantity (Universal/Particular).

The Rules of the Square of Opposition

To create a contradiction, you must flip both the Quality and the Quantity of the original statement:

• If the statement is Universal Affirmative (All A are B):
  The contradiction is Particular Negative (Some A are not B).
  Example: "All birds fly" ↔ "Some birds do not fly."


• If the statement is Universal Negative (No A are B):
  The contradiction is Particular Affirmative (Some A are B).
  Example: "No human is a stone" ↔ "Some humans are stones."

The 8 Unities (Al-Ittihadat al-Thamaniyah)

For a contradiction to be valid, the two statements must be talking about the exact same thing in the exact same way. Classical logicians mention 8 "Unities" that must be maintained, including:

1. Unity of Subject: You can't compare "Zaid is standing" with "Amr is not standing."
2. Unity of Time: You can't compare "It is raining today" with "It was not raining yesterday."
3. Unity of Place: You can't compare "It is hot in Cairo" with "It is not hot in London."

Why Does This Matter?

In debates, people often try to disprove a "Universal" claim by providing another "Universal" claim.
Wrong way: If someone says "All students are lazy," you don't have to prove "No students are lazy."
Logic way: You only need to find one student who is not lazy (Particular Negative) to shatter their entire argument.

Next Up: Conversion (Al-'Aks al-Mustawi)

What happens if you flip the Subject and the Predicate of a sentence? Does the truth stay the same? In the next post, we explore Logical Conversion—the art of flipping sentences without losing the truth.

Can you find the contradiction for the statement "All apples are red"? Write it in the comments!

Tags: #Logic #IlmAlMantiq #SquareOfOpposition #Contradiction #DebateRules #Philosophy