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).
