I need it in basic terms since Wikipedia is beyond me for a while. Thanks.
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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:
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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)
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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.
I.e..
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Major premise: All animals with wings are able to fly.
Minor premise: All pigs have wings.
Conclusion: All pigs can fly
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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).
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