(1) Either he aims too high or the cartridges are sometimes bad.
.'. Either the cartridges are not bad or he sometimes does not
aim too high. (0)
(O) Either care must be taken or telegrams will sometimes not be
correct.
.'. Either telegrams are correct or carelessness is sometimes
shown. (1)
§ 726. In the above examples the converse of E looks as if it had undergone no change but the mere transposition of the alternative. This appearance arises from mentally reading the E as an A proposition: but, if it were so taken, the result would be its contrapositive, and not its converse by negation.
§ 727. The converse of I is a little difficult to grasp. It becomes easier if we reduce it to the equivalent conjunctive—
'If the cartridges are bad, he sometimes does not aim too high.'
Here, as elsewhere, 'sometimes' must not be taken to mean more than 'it may be that.'
§ 728. Conversion by Contraposition of Complex Propositions.
As applied to conjunctive propositions conversion by contraposition assumes the following forms—
(A) If A is B, C is always D.
.'. If C is not-D, A is always not-B.
(O) If A is B, C is sometimes not D.
.'. If C is not-D, A is sometimes not not-B.