If one proposition is the negation of another, it followstrivially from the definition that the twopropositions are contradictories. The converse does not hold. Twopropositions can be contradictorieswithout either being the negation of the other. For example:
3) John is more than sixfeet tall
4) John is either exactlysixfeettall or elseless thansixfeet tall
are contradictories, but neither is the negation of the other. Negation is one way, but not the only way, of forming a contradictory.