Deductive reasoning (or *argument*) was first distinguished from Inductive
reasoning by Aristotle. He defined the difference between the two by
the direction of logical inference: deduction moved from universal (or more clearly known) propositions, to particular (less clearly
known ones), while he defined induction as the inference from particular claims to universal ones.

In contemporary Logic we define the difference based on *the logical status of the conclusion*: deductive arguments yield
*necessary* conclusions, while inductive arguments yield *probable* conclusions.

The success, and therefore the evaluation, of deduction is dependent on two distinct factors:

**Form**- is the structure correct?**Truth**- are the premises true?

If a deductive argument is valid ** AND** has all true premises, it is called a
sound argument.

For example:

**Valid -**
All dogs are cats.

Kato is a dog.

Therefore, Kato is a cat.

If we *assume* the truth of premises one and two the conclusion ** MUST** follow (

**Sound -**
All dogs are mammals.

Kato is a dog.

Therefore, Kato is a mammal.

The structure of this argument is identical to the first argument, so it is obviously **valid**. And, in this case the first premise is also
true, so this argument would be called **sound**.