Deductive Reasoning
See It in Action
Two examples of the idea done right—and one common look-alike that is not right.
EXAMPLE
EXAMPLE
NON-EXAMPLE
Definition
Deductive reasoning is the process of using logical steps, definitions, properties, postulates, and theorems to draw conclusions from given facts or statements.
Deductive reasoning is the process of reasoning from known facts, definitions, and accepted properties to reach a logical conclusion.
Key Characteristics:
It starts with general principles or known truths.
It uses logical steps to arrive at specific conclusions.
It is the basis for geometric proofs.
Example:
If we know:
All angles in a triangle add up to 180° (a known theorem),
Two angles in a triangle are 50° and 60°,
Then using deductive reasoning, we conclude:
The third angle must be 70°.
Deductive reasoning ensures that conclusions are logically valid and universally true when based on correct premises.