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Knowledge / Prior: should be constructed as an operator: "(know that) __" (see above) - does not "know __" - Prior: nevertheless: knowledge-that and knowledge-which has the same meaning - Solution: implicit. "He knows the answer to the question .." - For questions then there is the difference "if", "what" (various operators).
Objects of thought Oxford 1971
Arthur N. Prior
Papers on Time and Tense 2nd Edition Oxford 2003