Deductive Reasoning

We will discuss three types of reasoning : Deduction, Induction and Abduction, let's talk about Deduction.

Deduction is a type of reasoning that starts from the premises to reach a conclusion, without empirical tools, that is: just by pure reason. Consider the next argument.

A deductively valid argument
Premise 1: All Winged Animals Fly
Premise 2: Pegasi are Winged Animals
Conclusion: Therefore, Pegasi Fly

You may object, but the first premise is False, since the ostriches have wings and don't fly.

But this is not the point here. I have deliberately chosen an argument with a false premise, to show that the point of Deductive Reasoning, is not whether a premise or conclusion is true or false.

It is just about the possibility of inferring the conclusion given the premises are True.

Suppose the first premise is True : "All Winged Animals Fly", And suppose the second premise is also True : All Pegasi are Winged Animals.

Can you infer the conclusion?

Remember:
You can never claim that such and such is True by virtue of a deductively valid argument, Our argument being valid, does not make for the claim that Pegasi exist or that All winged animals fly.

Yes, If it is the case that ALL winged animals fly, and if Pegasi are winged animals, the it follows that Pegasi do, indeed, Fly…

That does not make our conclusion or premises true, it just makes the whole argument valid. So, Our Argument is valid since we can reach the conclusion given the premises are true.

That is Deductive Reasoning, just by means of pure reason (that is thinking in the bathroom if you will), you can determine whether an argument is valid or not.

Next we will talk about Inductive Reasoning.