All inexpedient acts are unjust.
.'. All just acts are expedient.
§ 522. Conversion by contraposition may be said to rest on the following principle—
If one class be wholly contained in another, whatever is external to
the containing class is external also to the class contained.
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§ 523. The same principle may be expressed intensively as follows:—
If an attribute belongs to the whole of a subject, whatever fails to exhibit that attribute does not come under the subject.
§ 524. This statement contemplates conversion by contraposition only in reference to the A proposition, to which the process has hitherto been confined. Logicians seem to have overlooked the fact that conversion by contraposition is as applicable to the O as to the A proposition, though, when expressed in symbols, it presents a more clumsy appearance.
Some A is not B.
.'. Some not-B is not not-A.
Some wholesome things are not pleasant.
.'. Some unpleasant things are not unwholesome.
§ 525. The above admits of analysis in exactly the same way as the same process when applied to the A proposition.