To test whether two propositions contradict, first express their full meanings and compare all relevant qualifications.
Checklist:
Same subject? Same predicate?
Same place? Same time?
Same potential/actual respect? Same condition?
Same part or whole? Same relational object?
A difference in a relevant qualification means the apparent negation no longer denies precisely the same claim.
“Ali was present in Lahore on Monday” and “Ali was not present in Karachi on Tuesday” contain affirmative and negative language, but both place and time differ. Contradiction has not been established.