Stony Brook University

necessary truths, but are contingent. Therefore, this demonstration cannot be a priori
demonstrable.
One of Leibniz’s typical proofs for the immortality of the soul can be found in
Confessio Naturae Contra Atheistas (1669). The proof is called Mentis humanae
immortalitas continuo sorite demonstrata (the immortality of the human mind
demonstrated by a continuous sorites). 32 The demonstration stems from Leibniz’s
criticism of the corpuscular philosophy, which holds that matter and motion can be
“explained” in entirely mechanical terms. The demonstration also depends on the claim
that thinking or perceiving is a non-material activity. It is not necessary to evaluate these
claims. A shortened version of the argument is sufficient to show what is formally at
stake in the demonstration.
To be demonstrated: The human mind is immortal.
1. The human mind is a being, one of whose actions is thinking.
2. Thinking is perceiving.
3. Perceiving does not involve parts.
4. Anything not involving parts does not involve motion.
5. Anything that does not involve motion is incorruptible (implied premise:
corruption is the motion of parts).
6. Anything incorruptible is immortal.
Connecting the subject of the first premise to the predicate of the last premise we can
conclude: ‘The human mind is immortal.’ Q.E.D. 33 While this argument is formally valid,
several premises appear quite questionable, a number of terms are left undefined, and it is
not certain that it does not depend on observations. Nevertheless, this is the sort of
argument Leibniz has in mind when he says that a true demonstration of moral doctrine
depends on proofs for God’s existence and the immortality of the soul. Yet it does not
seem to be an a priori proof.
The following is a good example of a demonstration in which moralistic
terminology is used for political purposes. It depends on both definitions of terms and
truths of fact. The demonstration is from Specimen Demonstrationum Politicarum pro
Rege Polonorum Eligendo (1669). 34 While the whole demonstration is some 60
propositions long, Leibniz provides a brief summary for those who may be “abused by
the length.”
1. Everything disgraceful/ugly diminishes honor.
2. What diminishes honor diminishes belief in power/force.
3. Whatever diminishes belief in power makes offense/attack easier to occur.
32 A.6.1.492 and LL 113. A sorites is a form of argument in which the subject of the first premise is
connected to the predicate of the conclusion by a chain of premises, each of which defines the predicates,
until the conclusion is reached (the proposition to be demonstrated).
33 As written: “Igiur MENS HUMANAS EST IMMORTALIS. Quod erat demonstrandum.” A.6.1.493
34 A Model of Political Demonstration on Behalf of Electing the King of Poland. This effort was written
under the pseudonym “Georgious Ulicovius Lithuanus,” at the request Leibniz’s employer, Baron
Boineburg. At the time of Polish succession, Boineburg wanted William-Phillipe Duke of Neuburg elected
in order to consolidate a Polish alliance with Germany against the French and Russians. Boineburg enlisted
Leibniz to present an argument for the Duke’s election, but the Duke was not elected.
151