Stony Brook University

Notably, this is essentially Leibniz’s late position, as well. In this (1697-1700) revision
note to the above passage, Leibniz clarifies and elaborates:
(1) that no derivative notion is to be accepted unless it is explained, and
(2) no derivative proposition unless it is proved. Explanation takes place
through definition, proof through syllogism, which provides a conclusion
by force of its form . . . and not everything necessary to the conclusion is
expressed, in order to avoid tedium. But it is no small matter to have a
way of reasoning infallibly on this basis if we do not avoid the effort
involved. The rules of Descartes are less adequate, however. Certainly the
first one—that what is perceived clearly and distinctly is true—is itself
untrue (unless it be restricted on some ground) and proves, not existence,
but only possibility. Nor is it very useful, unless we already have the
criteria of clearness and distinctness which I once stated in a study on truth
and ideas. (LL 91) 11
The “study” Leibniz refers to is his Meditationes de Cognitione, Veritate, and Ideis
(1684). Most important to note here is that both of these passages essentially characterize
the Euclidean geometric method he will often allude to, if not employ, in the Nova
Methodus and elsewhere: Definitions must be thoroughly analyzed to prove their
possibility, i.e., the logical compatibility of their concepts; and propositions must be
proven by demonstration; and demonstration consists of a chain of definitions. 12 In the
Nova Methodus, Leibniz is hardly this rigorous; but he refines his method considerably in
the Elementa Juris Naturalis, as we will see. Nevertheless, the definitions he does lay
down here in the Nova Methodus are extremely important, since they establish, among
other things, a normative distinction between “right” and “fact.” This distinction also
depends on the distinction between “real” and “nominal” definition, and more broadly,
corresponds with the metaphysical distinction between essence and existence. 13 I will
return to these points below and in subsequent chapters. But the point to bear in mind is
intended to refer. In any case, whether or not it agrees with Descartes, Leibniz’s position (better expressed
in his later formulation, below) must be born in mind: you cannot prove the existence of something from a
clear and distinct perception of it; you can only prove its possibility.
11 A.6.1.279. Z.9: “(1.) Ut nulla notio derivativa admittatur, nisi explicata, (2.) ut nulla propositio
derivativa, nisi probata. Explicatio fit per definitionem, probatio per Syllogismum vi formae concludentum
. . . neqve omnia ad consequentiam necessaria exprimantur taedii vitandi causa. Interim non exigua res est,
hac ratione habere nos modum infallibiliter ratiocinandi, si laborem non defugiamus. Regulae autem
Cartesianae minus sunt sufficientes. Certè illa prima: qvod clarè et distinctè percipio verum est, nec vera est
(nisi certa ratione circumscribatur), neqve enim existentiam sed tantum possibilitatem probat; nec valde
utilis est, nisi clari et distincti criteria habeantur qvae indicavimus aliqvando in schediasmate de veritate et
ideis.”
12 I will examine Leibniz’s demonstrative method in much more detail in Chapter Four.
13 These above passages show that Leibniz had always maintained that the existence of something cannot
be proven from its mere possibility as an idea. This may seem surprising and inconsistent with some of his
(later) major arguments, e.g., for the existence of a necessary being. However, I am interested only in how
his theory and use of definitions affects his attempts to establish “real” definitions (of right and justice) as
opposed to “nominal” and “arbitrary” definitions. This distinction between real and nominal definition is
absolutely central, at every point of his career, to the grounds of his claims for right, morality, and justice.
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