A difficulty arises when someone deliberately looks or listens and then immediately perceives something. Is that knowledge “necessary” because it does not result from argument, or “acquired” because a chosen act produced access to it?
The answer depends on the classification. Under the non-inferential criterion it may count as necessary; under a criterion focusing on intentional acquisition it may be considered acquired.
The terms are not contradictory when used in distinct technical senses. In careful analysis, a classification must be judged by the definition its author is using.