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Deductive Reasoning

What is it?

Deductive reasoning/thinking is a form of verbal or conceptual argument related to logic and reasoning. Deductive reasoning often employs, Syllogism to achieve its goal. Syllogism is a logical argument made up of a major premise, a minor premise, and a conclusion. Let's look at an example of a syllogism. Look at the slide of the universe and sun below.

All stars reside in the universe.


Syllogism Modeling

The above example is a powerful example of a deductive argument based on syllogismFirst, our major premise is factual and pretty irrefutable. Stars have been proven to only exist in the universe, whether that's metaphorically, conceptually, or literally. Second, our minor premise is also factual. Our sun is a star.  Third, our conclusion is based on sound logic. When creating a syllogisms, keep those parameters in mind. 

  • Major Premise (Use Absolute Fact Not Conjecture)

  • Minor Premise (Use Absolute Fact Not Conjecture)

  • Conclusion (Sound Logic Used) 

Because it may take some time to get good at building syllogisms, download the "Syllogism Creator Worksheet" to assist you in the process.

It should be noted that syllogisms aren't perfect. If the major or minor premises are false, you will end up with a conclusion that is faulty.


For example:


  • Major Premise - Everyone who eats cheese puffs is a computer programmer.

  • Minor Premise - Alley eats cheese puffs.

  • Conclusion - Therefore, Alley is a computer programmer. 

While the argument is valid (the model is being used properly), the logic is not. The logic is faulty because one of our premises are false. When a premise is false, the logic will be faulty. Using truthful premises is paramount to reaching accurate conclusions. 


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