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"about" / Prior: believing-that, thinking-that: never goes about propositions, but rather, what propositions are about. - "about" is systematically ambiguous; what it means depends on what kind of a name or quasi-names (eg numbers) follows.
Prior I 57f
"about" / Prior: instead of propositions about propositions (identity of propos E.g. "Bachelors ... "/" unmarried ... ") - better: "if someone expresses .."Bachelors...". he expresses the same propos. as "..unmarried ..." > this is not about propositions.
Prior I 155f
"about" / Unicorn: that a sentence is really about something (existent), cannot depend on the shape, because the shape is the same when the subject is fictional.
Objects of thought Oxford 1971
Arthur N. Prior
Papers on Time and Tense 2nd Edition Oxford 2003