|Geach, Peter T.
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Identity/GeachVsFrege: is not a relation - "Is an A" does not mean "has identity with A" - (whereby "A" is a name). - VsFrege: (in Frege, basic principles of artihmetics) instead of "There are just as many Fs as Gs": "Either any given object F iff it is a G, or there is a relation that is a one-to-one correspondence between the Fs and Gs". But this must not be an identity.
Identity/Geach: only objects can be strictly identical. - In terms, there is only analogous identity: if they are coextensive.
Identity/GeachVsQuine: Thesis: Identity is relative. - If someone says "x is identical to y", this is an incomplete expression. - It is an abbreviation for "x is the same as y". - (Weird, that Frege did not represent this).
Identity/tradition/Geach: can be expressed by a single schema.
(1)l- Fa (x)(Fx u x = a) - everyday-language: whatever is true of something which is identical with an object y is true of a and vice versa. - From this we derive the law of self-identity:
"l-a = a".
Because we take "Fx" for "x unequal a", then schema (1) gives us:
(2)l- (a unequal a) Vx(y unequal a u x = a) - this,of course, gives "l-a = a"
Identity/Geach: if we demand strict identity, regardless of the theory in which we move, we get into the semantic paradoxes such as Grelling's or Richard's solution: relative identity on theory or language, indissibility/"indiscernibility"/Quine -> Partial identity.
Tugendhat I 37
Identity/Dummett/Geach: "=" can only be used with reference to objects.
Logic Matters Oxford 1972
Vorlesungen zur Einführung in die Sprachanalytische Philosophie Frankfurt 1976
Philosophische Aufsätze Frankfurt 1992