(O) Some islands are not inhabited.
.'. Some islands are uninhabited (I).
CHAPTER VI.
Of Compound Forms of Immediate Inference.
§ 503. Having now treated of the three simple forms of immediate inference, we go on to speak of the compound forms, and first of
Conversion by Negation.
§ 504. When A and O have been permuted, they become respectively E and I, and, in this form, admit of simple conversion. We have here two steps of inference: but the process may be performed at a single stroke, and is then known as Conversion by Negation. Thus from 'All A is B' we may infer 'No not-B is A,' and again from 'Some A is not B' we may infer 'Some not-B is A.' The nature of these inferences will be seen better in concrete examples.
§ 505.
(A) All poets are imaginative.
.'. No unimaginative persons are poets (E).
(O) Some parsons are not clerical.
.'. Some unclerical persons are parsons (I).
§ 506. The above inferences, when analysed, will be found to resolve themselves into two steps, namely,