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are extrinsic.
C4. Intrinsic properties are not disguised relations to times ( modus
tollens , P9, P2).
P10. If intrinsic properties are those properties which ordinary things have
in the present, then there is no other time than the present; that is, presentism
is true.
P11. If presentism is true, then ordinary things do not persist.
C5. Presentism is false ( modus tollens , P11, C1).
C6. Ordinary things do not endure ( modus tollens , P9, C4, C5).
C7. Ordinary things perdure (disjunctive syllogism, C2, C6).
C8. The incompatible properties of ordinary things belong to their different
temporal parts ( modus ponens , P8, C8).
24
A Modern Modal Argument
for the Soul
Rafal Urbaniak and Agnieszka Rostalska
Alston , W. P. , and T. W. Smythe . β€œ Swinburne ’ s Argument for Dualism . ” Faith
and Philosophy 11 ( 1994 ): 127 – 33 .
Hasker , W. β€œ Swinburne ’ s Modal Argument for Dualism: Epistemically
Circular . ” Faith and Philosophy 15 ( 1998 ): 366 – 70 .
Nagasawa , Y. 2005 . β€œ Critical Notice of Richard Swinburne ’ s β€˜ The Evolution
of the Soul (Revised Version) ’ . ” Available at www.infi dels.org/library/
modern/yujin_nagasawa/soul.html (accessed 27 July, 2010).
Reames , K. β€œ A Response to Swinburne ’ s Latest Defense of the Argument for
Dualism . ” Faith and Philosophy 16 ( 1999 ): 90 – 7 .
Stump , E. , and N. Kretzmann . β€œ An Objection to Swinburne ’ s Argument for
Dualism . ” Faith and Philosophy 13 ( 1996 ): 405 – 12 .
Swinburne , Richard . The Evolution of the Soul . Oxford : Clarendon Press ,
1986 .
___. β€œ Dualism Intact . ” Faith and Philosophy 13 ( 1996 ): 968 – 77 .
Swinburne , Richard , and Sydney Shoemaker . Personal Identity . Oxford :
Blackwell , 1984 .
Urbaniak , R. , and A. Rostalska . β€œ Swinburne ’ s Modal Argument for the
Existence of a Soul: Formalization and Criticism . ” Philo 12 ( 2009 ):
73 – 87 .
Zimmerman , D. W. β€œ Two Cartesian Arguments for the Simplicity of the
Soul . ” American Philosophical Quarterly 3 ( 1991 ): 217 – 26 .
Just the Arguments: 100 of the Most Important Arguments in Western Philosophy,
First Edition. Edited by Michael Bruce and Steven Barbone.
Β© 2011 Blackwell Publishing Ltd. Published 2011 by Blackwell Publishing Ltd.
94 Rafal Urbaniak and Agnieszka Rostalska
Richard Swinburne, one of the most prominent representatives of dualism
in the twentieth century, formulated his modal argument for the existence
of the soul as an improvement of Descartes ’ (#76) analogous argument.
Roughly speaking, Swinburne argues that human beings currently alive
have nonbodily immaterial parts called souls, using the assumption that it
is logically possible that a human being survives the destruction of the body
(and a few additional supposedly quite innocent premises). The modern
twist to the argument that makes it technically interesting is that it employs
a quantifi ed propositional modal logic. The argument raises also a general
philosophical interest, like all seemingly simple and correct philosophical
arguments for strong conclusions.
The argument employs quantifi ed propositional modal logic T, a rather
straightforward extension of classical propositional logic. We extend the
language with two modal operators: β€˜ β—Š ’ read as β€œ it is possible that, ” and
β€˜ β–‘ ’ read as β€œ it is necessary that ” and quantifiers binding propositional variables.
On top of the classical rules of inference, one needs to add two axiom
schemata (called traditionally K and T):
(K) β–‘ ( A β†’ B ) β†’ ( β–‘ A β†’ β–‘ B )
(T) β–‘ A β†’ A
We also add two rules of inference: necessitation, which tells us that if
something is a thesis of the system, it is necessary, and propositional universal
quantifi er elimination, which works like universal quantifi er elimination
in classical predicate logic, except that it applies to propositional
variables and formulae. We ’ ll start with a brief presentation of the argument
in its original formulation. Then, we ’ ll reconstruct the argument in more
detail. Next, we ’ ll describe main known objections to the argument, describe
how one of the objections (usually considered to be lethal) can be avoided,
and fi nally, provide our own brief assessment of what we think the main
weakness of the argument is.
The argument was originally designed to prove that I [Swinburne] have a
soul in 1984, and I leave it in that form. Updating is always possible for any
year in which Premiss one is manifestly true. Likewise any name or other
referring expression can be substituted for β€˜ I ’ , so long as Premiss 1 remains
manifestly true. [ … ] I defi ne:
p = β€˜ I am a conscious person and I exist in 1984 ’
q = β€˜ my body is destroyed in the last instant of 1984 ’
r = β€˜ I have a soul in 1984 ’
s = β€˜ I exist in 1985 ’
x ranges over all consistent propositions compatible with ( p & q ) and
describing 1984 states of affairs.
A Modern Modal Argument for the Soul 95
β€˜ ( x ) ’ is to be read in the normal way as β€˜ for all x ’ .
The argument is then as follows:
p (Premiss 1)
( x ) β—Š ( p & q & x & s ) (Premiss 2)
∼ β—Š ( p & q & ∼ r & s ) (Premiss 3)
Premiss 2 says that it is possible that I survive into 1985, given that I am
conscious in 1984, even if my body is totally destroyed and whatever else
might be the case in 1984, compatible with these last two suppositions.
Premiss 3 says that it is not possible that I who am conscious in 1984 survive
into 1985 if my body is totally destroyed, unless there is a non - bodily part
of me in 1984, namely, a soul. It follows from Premiss 2 and Premiss 3 that
∼ r is not within the range of x . But since ∼ r describes a 1984 state of affairs
it follows that it is not compatible with ( p & q ). Hence ( p & q ) entails r . But
the addition to p of q , which describes what happens to my body at the end
of 1984 can hardly affect whether or not p entails r . So I conclude that p by
itself entails r . Hence, from Premiss 1, r . (Swinburne Evolution , 322 – 3)
Once we point out tacit assumptions, the argument comes out valid in
a rather modest modal logic T with universal propositional quantifi er elimination.