Relation
______________|_____________
| |
Compatible Incompatible
______|_____ _____|_______
| | | |
Subaltern Sub-contrary Contrary Contradictory.
§ 463. It should be noticed that the inference in the case of
opposition is from the truth or falsity of one of the opposed
propositions to the truth or falsity of the other.
§ 464. We will now lay down the accepted laws of inference with regard
to the various kinds of opposition.
§ 465. Contrary propositions may both be false, but cannot both be
true. Hence if one be true, the other is false, but not vice versâ.
§ 466. Sub-contrary propositions may both be true, but cannot both be
false. Hence if one be false, the other is true, but not vice versâ.
§ 467. In the case of subaltern propositions, if the universal be
true, the particular is true; and if the particular be false, the
universal is false; but from the truth of the particular or the
falsity of the universal no conclusion can be drawn.
§ 468. Contradictory propositions cannot be either true or false
together. Hence if one be true, the other is false, and vice versâ.
§ 469. By applying these laws of inference we obtain the following
results--
If A be true, E is false, O false, I true.
If A be false, E is unknown, O true, I unknown.
If E be true, O is true, I false, A false.
If E be false, O is unknown, I true, A unknown.
If O be true, I is unknown, A false, E unknown.
If O be false, I is true, A true, E false.
If I be true, A is unknown, E false, O unknown.
If I be false, A is false, E true, O true.
§ 470. It will be seen from the above that we derive more information
from deriving a particular than from denying a universal. Should this
seem surprising, the paradox will immediately disappear, if we reflect
that to deny a universal is merely to assert the contradictory
particular, whereas to deny a particular is to assert the
contradictory universal. It is no wonder that we should obtain more
information from asserting a universal than from asserting a
particular.
§ 471. We have laid down above the received doctrine with regard to
opposition: but it is necessary to point out a flaw in it.
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