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Relation-in extension/Prior: two-digit predicates can be associated in the same manner with relation-in-extension - E.g. Both: being-father-and-mother-of is not the same as both: be-greater-and-smaller-than but when the corresponding "relation-in-extension" are the same.
Relation: Richard thinks of Joan": relation (also sentence about two people) - but "Richard thinks that p": no relation - E.g. to think: - "someone is next door" no relation to anyone - (also not, when someone makes the thought come true) - thinking needs no object.
Thinking/Prior: needs no object: E.g. "someone is next door": no relation to someone - in the sense of "about" (about, aboutness) - E.g. someone has stolen my pencil "until I realize that I have lost it - solution/Prior: thinking - "of" one can think of something arbitrary, non-existent (or "of", "of", (later Vs) - but not thinking- "about" - (> Unicorn) - "of", "about" is ambiguous: I can also think that I think something of x and later learn that x does not exist, but that does not stop my thinking - Prior: but not difference "thinking in general" and "content"- Variant: "if I believe in the existence of x, I can think something of x": Vs: then someone who does not believe in it, cannot think that I think something of x.
Relation/Prior: belief no relation, otherwise relation to Cicero = Rel to Tullius - real relations have converse.
Objects of thought Oxford 1971
Arthur N. Prior
Papers on Time and Tense 2nd Edition Oxford 2003