Ayesha was ill on Monday / Ayesha was not ill on Thursday are compatible: recovery is possible. Replace Thursday with Monday, keep the same sense of illness and relevant circumstances, and you obtain genuine contradiction. The negative word was unchanged; the time reference determined the difference.
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Worked example: different time
Contradiction and the Eight Conditions
Ayesha was ill on Monday / Ayesha was not ill on Thursday are compatible: recovery is possible. Replace Thursday with Monday, keep the same sense of illness and relevant circumstances, and you obtain genuine contradiction. The negative word was unchanged; the time reference determined the difference.