Deductive Reasoning

Deductive reasoning is a kind of skill and it has been a part of human thinking for centuries and is used all the time in our daily life activities. Deductive reasoning helps to conclude that a particular statement is true, as it is a special case of a more general statement that is known to be true. For example, once we prove that the product of two odd numbers is always odd, we can immediately conclude the product of 34523 and 35465 is odd because 34523 and 35465 are odd numbers.

Deductive Reasoning Example

Deductive reasoning is one of the main logical tools that helps to establish the truth of an unambiguous statement. Now, let us understand what is deductive reasoning with the help of examples

For example, you are provided with four cards. In each card, a number is printed on one side and a letter is printed on the other side.

Deductive Reasoning Example

Also, you are provided with a rule that these cards follow:

The rule is “If a card has an even number, then it has a vowel on the other side”.

The given statement represents that the card with an even number has a vowel on the other side. But, it does not state that a card with a vowel on one side has an even number on the other side. Also, the rule does not state that a card with an odd number on one side must have a consonant on the other side. Now, let us start checking the cards one by one.

We do not need to turn over the cards “A” and “5”, as the rule still holds.

But, we need to turn over the card V and 6. If card V has an even number on the other side, then the rule has been broken. Similarly, if card 6 has a consonant on the other side, then we can say that the rule has been broken.

This method of reasoning to solve a puzzle is called deductive reasoning. This process is called deductive reasoning because we have arrived at a result of a statement from the previously established statements using logic.

Consider another example, “The flower Solaris blooms, only if the maximum temperature is above 28°C on the previous day” and also the other statement given is “Solaris bloomed in Imaginary valley on September 15th, 2005. Hence, by using deductive reasoning, we can conclude the statement that “The maximum temperature in Imaginary valley on September 14th, 2005 was above 28°C”.

Try yourself:

Use deductive reasoning and answer the following:

  1. Humans are mammals. All mammals are vertebrates. Based on the two statements, what will you conclude about humans?
  2. Gulag is a Martian. Martians have red tongues. Based on the two statements, what will you conclude about Gulag?

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