[hist-analytic] Knowing that I know a Necessary Truth

Danny Frederick danny.frederick at btinternet.com
Sat Jan 1 16:12:53 EST 2011

Hi Roger,

Definite descriptions have different logical properties to names, so it
should not be surprising that by substituting a definite description for a
name you can turn a valid argument into an invalid one. In particular, a
name is a rigid designator, whereas a definite description usually is not;
and this means that the two types of expression, even if they happen to
denote the same thing, cannot generally be swapped in modal contexts.

There is much wrong with your argument. First, there is confusion of use and
mention. Hesperus names nothing. 'Hesperus' names Hesperus. Second, we
cannot discover that two objects are one, though we might discover that two
names denote the same thing (I suspect this confusion depends upon the first
one). Third, it is false that it might not have been the case that Hesperus
= Phosphorus (assuming the thing exists). Your conclusion follows from your
premises only because the premises are self-contradictory.


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