Deductive reasoning and syllogism


I need it in basic terms since Wikipedia is beyond me for a while. Thanks.

In: 4

Hi /u/Ice-Guardian!

Deductive reasoning is a method of argumentation which is in contrast to inductive reasoning.

Where inductive reasoning is of empirical nature, i.e. it looks at specific observations and constructs evidence-based arguments from them, deductive reasoning is an abstract, generalizing form of argument based on the internal logic.

That is, deductive arguments are based on axioms or premises – that is, statements that are assumed to be true without proof. From these premises, logical conclusions are drawn.

In particular, a syllogism consists of two premises, the major premise, which is a general statement, and the minor premise which is a more specific statement. From these two premises, a logical conclusion is reached.

Let’s look at an example:

Major premise: All animals are mortal. (A general statement)
Minor premise: All humans are animals. (A specific statement)

Conclusion: All humans are mortal. (A logical conclusions of the two premises above)


Note here, that the validity of deductive arguments is **only** concerned with its internal consistency, *not with the truth value of the premises*. I.e. a syllogism which is logically consistent but based on wrong premises is still *valid* within a deductive reasoning framework.


Major premise: All animals with wings are able to fly.
Minor premise: All pigs have wings.

Conclusion: All pigs can fly


is a valid syllogism, despite the fact that the premises are wrong.

Due to the requirement of logical consistency, deductive reasoning systems are non-ampliative (that is, the conclusion is implicit in the premises, no new information is achieved in the conclusion that was not already present in the premises) and truth-preserving (**if** the premises are true, the conclusion is also true).

Does this answer your question?