Statement 1: This horse runs fast.
Statement 2: That horse does not run fast.
Not necessarily contradictory: two different horses may be intended. Both can be true. If the very same horse, speed criterion, and circumstances are fixed, affirmation and denial of the same predicate do contradict.
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Worked example: different subject
Contradiction and the Eight Conditions
Statement 1: This horse runs fast.
Statement 2: That horse does not run fast.
Not necessarily contradictory: two different horses may be intended. Both can be true. If the very same horse, speed criterion, and circumstances are fixed, affirmation and denial of the same predicate do contradict.