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Measuring / analogy / intentionality / belief / Brentano / Field: the idea is that the explanation is based not on relations like "x has mass in kg r" between physical objects and non-physical numbers, but in some "intrinsic relations" between physical objects themselves. e.g. "The mass of x is the sum of the masses of y and z". - Then Brentano’s problem has been solved - but we have to make strong assumptions about the internal structure of mind states. - Differently: Dennett: Here numbers can not be attributed to physical objects but to monadic properties - the property to have a certain mass.
Realism, Mathematics and Modality Oxford New York 1989
Truth and the Absence of Fact Oxford New York 2001
Science without numbers Princeton New Jersey 1980