The Elegant Magister i o ithe two basic principles of Leibniz and Wolff, namely the principle of con¬
tradiction and the principle of sufficient reason. The first, which amounts
to the claim that it is impossible for the same thing to be and not to be at
the same time, is really just the definition of the impossible, and is subor¬
dinate to the principle of identity. Indeed, the principle of identity would
be the basic principle, if it were one principle, but Kant argued that it re¬
ally consists of two: the principle "whatever is, is," which holds for positive
truths, and the principle "whatever is not, is not," which holds for nega¬
tive truths. Nevertheless, the principle of contradiction is a basic principle
in the sense that it is irreducible and necessary, even if it is not the very first
principle.
In the same way, Kant modified and defined the principle of sufficient
reason. Calling it, with Christian August Crusius, the principle of deter¬
mining reason, he rejected Wolff's definition of it as circular, raised a
number of difficulties with regard to it, but ultimately defended it. In par¬
ticular, he addressed Crusius's claim that this principle leads to the "Stoic
fate," thus "impairing all freedom and morality." This argument was not
new, but Crusius had put it forward "in greater detail and more force¬
fully."^6 Therefore, the principle of sufficient reason had to be defended
anew. Kant did so at length, thus endorsing again one of the basic tenets
of Leibnizian philosophy. Rejecting two other principles that were usually
thought to follow from the principle of sufficient reason, he offered two
principles of his own: (i) the principle of succession, that is, substances
can change only insofar as they are connected to other substances; their
reciprocal dependence determines how much they change; and (2) the prin¬
ciple of coextension: "finite substances by their mere existence are unre¬
lated," and they are related only insofar as they are maintained by the will
of God as the common principle of their existence. The divine intellect
maintains them "in a systematic pattern of mutual relations."
Kant meant to offer a new system. He called it "the system of the uni¬
versal connection of substances." It can do justice to what is correct in the
theory of physical influx as well as to what is correct in the theory of pre-
established harmony, but it should not be identified with either. This dis¬
sertation thus represented in an important sense the promised sequel to the
Living Forces. Kant tried to show how efficient causality with regard to the
external relations of substances is compatible with changes "that happen
internally" and are based on internal principles. Efficient causality repre¬
sents dead forces, the internal changes represent living forces, but God ul¬
timately is the source of both, and God keeps them in harmony.