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|Epistemic Logic||I 11
Epistemic Logic/Standard/Hintikka: there are usually extremely many alternatives that are compatible with what a person b knows.
But it is not necessary to demand that all such worlds are really within the domain of permitted alternatives.
Epistemic Logic/Hintikka: it is not clear how we should assess the situation
A) Vs Restriction of the individual domain: since the restriction can hardly be avoided in alethic standard modal logic, this is again an argument against the possibility of alethic modal logic.
B) one could affirm the idea that not all epistemic and doxastically possible worlds must be logically possible.
Epistemic Logic/Hintikka: epistemic logic is usually regarded as a branch of modal logic.
Semantics of possible worlds/possible world/semantics/Hintikka: semantics of possible world is a misleading term for the semantics of epistemic logic.
Epistemic Logic/Hintikka: most of the work focuses on syntactic questions and deductive techniques. This is a mistake.
One should focus on semantic (model-theoretical) questions.
Epistemic Logic/Laws/Hintikka: the basic laws are obtained by a simple idea:
Definition knowledge/Hintikka: knowledge is what enables the knowing person to concentrate on the subset W1 of the set of all worlds W.
W1: W1 is then relative not only to the knowing person b, but also relative to the scenario w0 ε W.
Definition b knows that S iff. S is true in all epistemic b alternatives.
Uniqueness condition/W-questions/response/Hintikka: the condition that something is a complete and unambiguous answer to a who-question (ambiguous, see above) is first that (8) has to imply (7)
(6) Who is the man over there?
(7) I know who the man is over there
E.g. it is Sir Norman Brook.
(8) I know that the man there is Sir Norman Brook.
Problem: the step from (8) to (7) is that of an existential generalization (EG).
Problem: For that, we need an additional premise. E.g.
(13) (Ex) Ki (Sir Norman Brook = x).
(Non-mirrored quantifier, perceptually)
"I know who Norman Brook is."
Epistemic Logic/Criterion/Hintikka: with this the epistemic logic freely provides an additional criterion for complete answers.
N.B.: this applies to both methods of identification (public/perspective).
Uniqueness condition: for the fact that e.g. "the man over there" is a clear and complete answer to (9):
(14) (∃x) Kl (that the man there = x)
That is, that the man who is shown counts as aquaintance of the one who is asking the questioning.
Jaakko and Merrill B. Hintikka
The Logic of Epistemology and the Epistemology of Logic Dordrecht 1989
J. Hintikka/M. B. Hintikka
Untersuchungen zu Wittgenstein Frankfurt 1996