III
1. The Principle of Plenitude and the Plurality of
Worlds.
According to Lovejoy ([1936], Ch. IV), the
Renaissance idea of a
plurality of inhabited worlds in
a physical universe infinite in space owes
more to the
persisting force of the principle of plenitude than to
the
new Copernican astronomy. The doctrine of an
infinity of worlds, as put
forward most notably by
Giordano Bruno, is associated with his interest in
the
new astronomy; but it is equally true that this doctrine,
as well
as the hypothesis that there is life on these
worlds, could not be deduced
from astronomical data
alone. The argument of which Bruno avails himself
is
clearly a development of the principle of plenitude.
We may not
think that a finite effect comes from an
infinite cause; in God, and
therefore in the temporal
order that derives from Him, the possible and the
real
coincide. Divine power cannot remain idle, divine
goodness cannot
but be infinitely diffused, being infi-
nitely communicable. God, then, is a fertile father
(padre fecondo), endowed with an illimitable genera-
tive capacity (capacissimo di innumerevoli mondi),
as found in De l'infinito universo 
e 
mondi (1584),
Dial. I.
Descartes' authority, in the course of the seventeenth
century, lends
support to this rejection of the idea of
the universe as a finite and
self-contained sphere; and
the idea of a plurality of inhabited worlds is
given great
currency in Fontenelle's Entretiens sur la
pluralité des
mondes (1686).
2. The Full Universe of Leibniz.
The diffusion of
the idea of a Chain of Being in
eighteenth-century
thought was certainly and decisively aided by the
success of Leibniz, a great advocate of the principle
of plenitude and
continuity, which he posited as a
correlative of the principle of
sufficient reason. Leib-
niz, in one of his
letters to Samuel Clarke (1715-16),
writes:
The least corpuscle is actually subdivided infinitely, and
contains
a world of other creatures, of which the universe
would be
deprived, if that corpuscle were an atom, that
is, a body of one
entire piece without subdivision. In like
manner, to say that there
is a vacuum in nature would be
to attribute to God a most imperfect production; it
would
be to violate the great principle of the necessity of a suffi-
cient reason...
(Leibniz Selections, p. 236).
And elsewhere (De synthesi et analysi universali)
the
principle of sufficient reason, whence flows, among
other things,
the fullness of the universe, is defined as
one of the greatest and most
fertile truths of human
cognition, since it assures us that all truths,
even the
most contingent, have an a priori proof,
i.e., a reason
for which they are rather than are not. This bond had
already been established by Leibniz in the Elementa
philosophiae arcanae (1676): the principle of the har-
mony of things requires that there exist the
greatest
possible quantity of essence. There is no gap among
forms; it
is not possible to find an empty space or time.
Every particle of matter
contains infinite creatures (cf.
also the so-called First Truths, Primae veritates [1686]).
The argument is drawn out at length in two other
writings of Leibniz:
De rerum originatione radicali
(1697) and
the Principes de la nature et de la
grâce
(1718, posthumous). “Not only in no one
of the singular
things”—writes Leibniz in the first
of these, “but nei-
ther in the whole
aggregate and series of things, can
one find a sufficient reason for their
existence (nam
non tantum in nullo singulorum, sed nec
in toto aggre-
gato serieque rerum
inveniri potest sufficiens ratio ex-
istendi). The world's reasons must therefore be sought
in something extra-worldly, different from the succes-
sion of states, or series of things, the aggregate of
which
constitutes the world (rationes igitur mundi in
aliquo
extra-mundano, differente a catena statuum, seu serie
rerum, quarum aggregatum mundum constituit).” We
must go back, then, from the physical necessity of
things to their
metaphysical necessity—which would
be precisely their sufficient
reason. Leibniz goes on:
In possible things, or in their very possibility or essence,
there is an
exigency to exist, or (so to speak) claim to exist;
in a word,...
essence of itself tends towards existence.
Whence it follows that all
possible things... tend with
equal right towards existence in
proportion to their quantity
of essence or reality, or according to the
grade of perfection
they contain; for perfection is nothing but the
quantity of
essence.
Thus, given only that there is a reason for the passage
from possibility to
actuality, it will follow that a maxi-
mum of
reality will be actualized. In other words every
possibility has an
“impulsion (conatus) to be real”;
and
the sole restriction in the passage from the possible
to the
actual is that imposed by the criterion of “com-
possibility,” the
reciprocal compatibility of possi-
bilities. From the conflict of all the possibilities which
severally
seek existence, the result will be the existence
of the maximal series of
all possibilities.
The argument is taken up again in the Principes,
in
relation to the problem of the monads. All is full
in nature; every monad
is a living mirror that reflects
the universe; and there is an infinity of
degrees in
monads, les unes dominant plus ou moins sur
les autres
(ibid., pp. 3-4). The sufficient reason for the
existence
of the universe cannot reside in the series of contingent
things, but only in God, from whose perfection it
follows that from the
impulse towards existence proper
to all essences, the most perfect of
possible worlds will
result. Without that we should be unable to say
why
things are, and why they are as they are (ibid., pp.
7-10).
3. Ethico-political Consequences of the Idea of the
Chain of Being in the Eighteenth Century.
It is Leib-
niz, as we know, who draws
from the idea of a Chain
of Being, and particularly from the principle of
pleni-
tude, those optimistic consequences
already implicit—
consequences which for that matter did not
escape
others before him, for example, Giordano Bruno (cf.
De immenso [1591], II, 13). Already in the
De rerum
originatione radicali (1697),
Leibniz passes from the
principle of sufficient reason to the perfection of
the
world:
... from what has been said it follows that the world is
most
perfect, not only physically, or, if one prefers, meta-
physically, because that
series of things has been produced
in which there is actually a
maximum of reality, but also
that it is most perfect morally....
The world is not only
the most admirable mechanism but insofar as
it is composed
of souls, it is also the best republic, through
which the
greatest measure of happiness and joy is conferred
upon
these souls, in which their physical perfection consists
(Leibniz Selections, p. 351).
Experience seems to show the opposite: particularly
if we consider the
conduct of mankind, the world seems
rather chaotic than ordered by a
supreme wisdom. But,
objects Leibniz, it is not fair to judge the whole
by
the part. We know only a small part of an eternity
infinitely
extended, namely the extent of the memory
of a few millennia handed down by
history. And yet
from such scant experience we rashly judge what is
immense and eternal. It is as if we were to examine
a tiny portion of a
painting and discern there nothing
but a confused mass of colors without
design and with-
out art. In the universe, in
short, the part can be
disturbed without prejudice to the whole, which
will
inevitably escape whomever, like man, has only a
partial vision
of things. The theme is taken up again
by Leibniz on many occasions in the
Théodicée (1710)
and in the
Principes (1718).
We have seen how the principle of plenitude—by
virtue of which
all possible things pass into actual
existence (the criterion of
compossibility being the only
limiting factor)—was connected, in Leibniz, with
that
of sufficient reason. Of this latter principle Lovejoy
([1936],
pp. 145-49, 165-80) gives an interpretation
intended to show its affinity
with Spinoza's kind of
determinism. According to Lovejoy, the principle
of
sufficient reason, with its criterion of compossibility as
sole
restriction in the passage from the possible to the
actual, is not
substantially different from the universal
necessity of Spinoza; and
absolute logical determinism
would then be characteristic of the thought of
both.
This interpretation of the principle of sufficient rea-
son and of the consequent justification of moral and
physical
evil helps clarify the special nature of Leib-
nizian “optimism,” and in general of eighteenth-
century optimism of
Leibnizian derivation; and also
helps explain how it could coexist with a
description
of man's place in the universe which certainly does
not
seem, at first, to encourage an optimistic vision
of the human condition.
It was not a question of deny-
ing the existence
of evil but rather of showing the
necessity for it—and this was
done in the face of the
most dismal and grim descriptions of a natural
and
moral reality in which this same passage from possi-
bility to reality shaped up as a struggle for
existence.
This is a recurrent motif in the theological and moral
writings of the time, and there is an echo of it in Pope's
Essay on Man (1734), a great popularizer of the idea
of the Chain of Being and its implications. The contrast
between such
avowed optimism and this taste for the
grimmest descriptions of the human
condition did not
escape Voltaire, the most famous critic of the
optimism
of his day: Vous criez “Tout est
bien” d'une voix lamen-
table, he observed; and he invited his adversaries to
cease proposing the immutable laws of necessity as
explanation of evil.
In this plan of a perfect universe in which outrageous
(and necessary)
afflictions of individuals are embraced
and given a new value in the law of
universal harmony,
a not inconsistent feature was the idea that man,
far
from being the king of creation and the measure of
all things, was
a mere link in the Chain of Being,
infinitely farther from the highest
grades of creation
than he is above the lowest of creatures. This too
is
a recurrent motif in the literature of the time.
An argument in favor of political conservatism fol-
lowed from all of this: if the perfection of the divine
plan
requires a universe ordered in a hierarchy of
beings, each destined to
occupy a place in the scale
of creatures so that all gradations are filled,
then the
same law should prevail in the world of men, or the
moral
universe: the norm of behavior should be to live
in keeping with one's
condition, without subverting any
order of society which, like a microcosm,
reflects the
very order of the universe.
