It's
said by some (or most) logicians that “logic
must handle every possible state of affairs” and hence
that it “can't imply the
existence of anything” (Dale
Jacquette). That almost sounds like a non sequitur.
Yes, logic must handle “every possible state of affairs”.
Nonetheless, how does it follow from this statement that logic can't
imply the existence of anything? Why can't logic be able to
handle every state of affairs and imply the existence of
something (or one thing)?
Is
it because if logic is applicable to everything, then implying
the existence of something would pollute its ability to handle
all states of affairs (note the jungle of quantifiers here)? Or
is is it that the case that something (or these things)
would somehow make logic contingent (or empirical) in nature?
Nonetheless, implying (or allowing) the existence of something
that's contingent (or empirical) isn't the same as arguing that logic
itself is contingent (or empirical). Logic can still be applied
to the the contingent (or empirical) even if isn't itself contingent
(or empirical).
Does
it mean, instead, that if logic implies the existence of anything
(or even something) that it would somehow depend on
that something? And, if logic did imply the existence of
anything, then its logical purity would somehow be sullied?
In
that sense, quantificational
logic (or first-order logic) is far from being pure.
Quantifiers
in logic have existential
import (or have ontological
commitment). That is, a quantificational proposition is
about the existence (or non-existence) of something (or of
many things). Even free
logic accepts abstract
objects of various kinds. It can also be said that logical
statements about self-identity
have existential import. That is, the proposition
(x) (x = x) has existential implications. And,
more obviously, so too does, (∃y) (y = y).
It
seems to follow from the acceptance of quantificational logic that an
empty
universe is excluded – nay,
it's logically impossible. However, do these facts about
quantificational logic necessarily apply to the more generic “logic”
we began discussing? Perhaps quantificational logic is actually a
deviant
logic!
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