Relation-Theory: takes belief to be a relation to internal objects (entities). Virtually all authors are against the assumption of thoughts as internal objects. See also intensional objects, intensions, propositional attitudes, mentalism.
Relational Theory/Bigelow/Pargetter (Science and Necessity Cambridge University Press 1990 p55) assumes universals (e.g. sets, numbers, properties) and relations between them in order to explain the problem of quantities. See also change, motion, quantities, universals, Platonism, nominalism.
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Conviction / error / deception / Davidson: beliefs have no objects that could match with reality (representations) but causes - these are publicly (intersubjective) accessible objects - ((s) the meanings that play a role in convictions shall be individuated by the public objects - (the causes)).
Der Mythos des Subjektiven Stuttgart 1993
Handlung und Ereignis Frankfurt 1990
Wahrheit und Interpretation Frankfurt 1990