Types of Arguments- Deductive reasoning

Deductive reasoning is the drawing of a specific conclusion from one or more general premises – meaning that it starts with a series of assumptions, which may have greater or lesser degrees of acceptance between the arguing parties, and observations.

Jeff wants his mother Tammy to stop smoking. He tells Tammy that smoking has undesirable health consequences, is an unattractive habit and creates an odor that pervades the whole house, making it unpleasant to live in. Using these general reasons he concludes that Tammy, specifically, should stop smoking.

Deductive reasoning is generally recognized as a robust form of reasoning, because if the premises are true, it guarantees that the conclusions will also be true. It is subject to a particular quirk, though: it is possible for a deductive argument to be internally consistent and still have the conclusion be out of sync with reality if the premises were themselves invalid. It also rests on the belief that the premises are universally applicable, and applicable to the case being argued for in particular.

As a result, it is up to you to check the applicability and truth of your premises if you are going to make a deductive argument. Of course, this internal consistency also means that it is possible to pull a fast one over your opponent by purposefully using incorrect or non-universal premises to make your argument – if they are ignorant of the truth, they may be forced to agree with you. The ethicality and pitfalls of this type of strategy has already been discussed. Use it to your advantage only when absolutely necessary. It is better to base your arguments on valid and universal premises anyway.

Another potential use of deductive reasoning, one also arising from its internal consistency is to test the validity of premises, or of inductive conclusions, which we will look at shortly. The premises are taken at face value, extrapolated to their logical conclusion and then checked against reality. If the conclusion is consistent with reality, the premises are valid. Otherwise, they are not.

This is the method used by scientists to test whether theories and hypotheses are true: drawing conclusions about how the natural world should act if they are true and then comparing those conclusions with their observations. In your own debates with people around you, you can use it to break down your opponent’s assumptions and inductive arguments.