There are two types of logical inferences; induction and deduction.
Inductive reasoning aims at developing a theory while deductive reasoning aims at testing an existing theory.
1. Inductive Reasoning
a) From specific sample to the general principle
- Generalisation
'My older brother is good at math. My friend's older brother is good at math. My neighbour's big brother is a math tutor. Therefore, all older brothers are good at math.'
Rule: Greater the sample; the stronger the argument.
b) Effect to Cause
Modus Ponens: if p THEN q, p THEREFORE q
[ Premises THEREFORE Conclusion= Argument]
When it rains (cause) THEN the street gets wet (effect), the street is wet (effect), THEREFORE it must have rained (cause).
Note: There can be other causes to specific effect, maybe they have washed the streets.
Therefore inductive argument can be called a strong argument.
2. Deductive Reasoning
a) From general principles to a specific conclusion
For example, the inference from the premises "all men are mortal" and "Socrates is a man" to the conclusion "Socrates is mortal" is deductively valid.
b) Cause to effect
[ Premises THEREFORE Conclusion= Argument]
Modus Ponens: If p THEN q, p THEREFORE q
When it rains (cause) THEN the street gets wet (effect), it is raining (cause) THEREFORE the street will be wet ( effect).
"Cause" has determined "effect or effects" therefore deductive arguments are valid.
Rule: If all premises are true, then the conclusion is also "true" in the case of a deductive argument.