What would become of this assertion, if, assuming in my turn the
offensive, I should demonstrate that belief in the existence of
bodies, or, in other words, in the reality of a purely corporeal
nature, is untenable? Matter, they say, is
impenetrable.--Impenetrable by what? I ask. Itself, undoubtedly;
for they would not dare to say spirit, since they would therein
admit what they wish to set aside. Whereupon I raise this double
question: What do you know about it, and what does it signify?

1. Impenetrability, which is pretended to be the definition of
matter, is only an hypothesis of careless naturalists, a gross
conclusion deduced from a superficial judgment. Experience shows
that matter possesses infinite divisibility, infinite
expansibility, porosity without assignable limits, and
permeability by heat, electricity, and magnetism, together
with a power of retaining them indefinitely; affinities,
reciprocal influences, and transformations without number:
qualities, all of them, hardly compatible with the assumption of
an impenetrable aliquid. Elasticity, which, better than any
other property of matter, could lead, through the idea of spring
or resistance, to that of impenetrability, is subject to the
control of a thousand circumstances, and depends entirely on
molecular attraction: now, what is more irreconcilable with
impenetrability than this attraction? Finally, there is a
science which might be defined with exactness as the SCIENCE OF
PENETRABILITY OF MATTER: I mean chemistry. In fact, how does
what is called chemical composition differ from penetration?[5].
. . . In short, we know matter only through its forms; of its
substance we know nothing. How, then, is it possible to affirm
the reality of an invisible, impalpable, incoercible being, ever