Immediate Inference - Eduction

is a type of immediate inference in which we deduce the truth of other propositions with a different structure from a given proposition.

Rule:  Particular terms cannot be turned into universal. What is true to some may not be true to all.

For example:

                All men are mortals.

From this proposition, I can deduce an apparently equivalent proposition: Some mortals are men, but NOT all mortal are men.

Remember that we do not give additional knowledge when we deduce propositions from a given proposition when we use eduction. In fact, all other new propositions deduced from a given proposition are not something new. In meaning, they are the same with the original proposition.

Kinds of Eduction:

1.       Conversion – it is done by simply interchanging the subject and the predicate. We call the original proposition convertend, and the new proposition converse.

Examples:

Convertend                                                                        Converse

All men are mortals.                                                       Some mortals are men.

Some politicians are liars.                                             Some liars are not politicians.

No stones are flowers                                                   No flowers are stones.

Some animals are not mammals.                              no converse

2.       Obversion – it is done by changing the quality of the proposition (from affirmative to negative, from negative to affirmative) and replacing the predicate with its contradictory. We call the original proposition obvertend, and the new proposition obverse.

Examples:

Obvertend                                                                          Obverse

All men are mortals.                                                       No men are non-mortals.

Some politicians are liars.                                             Some politicians are not non-liars.

No stones are flowers.                                                  All stones are non-flowers.

Some animals are not mammals.                              Some animals are non-mammals.

3.       Contraposition 1 – It is done by doing obversion, and then conversion. We call the original proposition contraposend  and the new proposition contraposit 1.

Examples:

Contraposend                                                                   Contraposit 1

All men are mortals.                                                       No non-men are mortals.

Some politicians are liars.                                             no contraposend 1

No stones are flowers.                                                  Some non-flowers are stones.

Some animals are not mammals.                              Some non-mammals are animals.

4.       Contraposition 2 – it is done by doing obversion, then conversion, then obversion again. We call the original proposition contraposend and the new proposition contraposit 2.

Examples:

Contraposend                                                                   Contraposit 2

All men are mortals.                                                       All non-men are non-mortals.

Some politicians are liars.                                             no contraposend 2

No stones are flowers.                                                  Some non-flowers are not non-stones.

Some animals are not mammals.                              Some non-mammals are not non-animals.