The logic of knowledge and demonstratives
Date
2020-08
Authors
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Publisher
Tartu Ülikool
Abstract
The thesis aims to demonstrate how an epistemic operator K can be added
to the Logic of Demonstratives. I started with a description of Kaplan’s LD. First
off, I showed two reasons motivated Kaplan to create the formal system LD. There
are several contingent logical truths in LD but one of them φ↔Aφ played a crucial
role in my further reasoning. In the second section of the thesis, I tried to add the
epistemic operator K to the LD using its standard definition. As a result, I got a
formula (K+A) that leads to a number of weird results. For example, If it is known
that φ↔Aφ then every truth is known. I argue that LD is inconsistent with the
standard interpretation for K. However, Rabinowicz and Segerberg(1994) provide
the non-standard interpretation of epistemic operator K. They consider necessity
and actuality operators as ones with a fixed perspective and allow K to have a
variable perspective. As a result, their definition of K might be directly added to
LD without creating the troublesome formula (K+A). It helps to avoid all the
problems from the second section That’s why I conclude that we can have the Logic
for Knowledge and demonstratives (LD+K) and treat it like a possible extension
of LD. This conclusion equips us with a formal tool to analyze sentences like ‘It is
known that I am here now’ that was unanalyzable in the original formal system.
Description
Keywords
philosophy, logic, epistemology