a. CONTRADICTORY – one of which expresses a positive conceptual reason or formal feature, and the other is negation.
EXAMPLE: White or non – white; Living or non – living.
Between them no intermediate or alternative is possible. a man is either living, or non – living: he may be dying but he is still living.
RULE: one is necessarily true, and the other is necessarily false. Hence, both cannot be affirmed, or denied at the same time of the same thing. If one is affirmed, the other is denied; and vice versa.
E.g., the plant is alive. Therefore, it is not non – alive. The stone is non – alive. Therefore, it is not alive.
b. CONTRARY – concepts that express conceptual reason or formal features which are opposed to each other as extremes in a certain order or class.
EXAMPLE: rich and poor; black and white; clever and stupid.
Between such extremes there are many intermediates possible: a man may neither be white, nor black, but brown; he may not be clever nor stupid, but average.
RULE: both cannot be true; but both can be false. Hence, if one is affirmed, the other must be denied. But, if one is denied, the other is doubtful: it may be affirmed or denied.
E.g., this paper is white; therefore, it is not black. It is not black; it is doubtful if it is white. It cannot be white and black at the same time; but it may not be white nor black.