In the middle ages 203

heart of change. It is not only the accidents

which change when, for example, the oak grows,

or its wood hecomes tougher, or its place changes

when it is transplanted, or its activities are re-

newed as it develops ; but the very substances them-

selves are carried into the maelstrom of change,

arid nature makes us witness to the unceasing spec-

tacle of their transformations. The oak dies; and

from the slow work of its decomposition are born

chemical bodies of most diverse kinds. An electric

current traverses the molecule of water ; and behold

hydrogen and oxygen arise.

All of this is essentially scholastic doctrine.

When one substance changes into another, each

has a quite different specificity. Substances differ

not in degree but in kind. An oak never changes

into another oak, nor a particle of water into an-

other particle of water. But out of a dying oak, or

a decomposed particle of water, are born chemical

bodies, which appear with quite different activities,

quantities, relations, and so on.^ The differences

of all these activities, quantities, and the rest, are

for us the only means of knowing the substances of

things, because the activity of a thing gives its!

measure of perfection and springs out of it : "agere '

sequitur esseJ" And hence corresponding to irre-

3 "There is not the slightest parity between the passive and the

active powers of the water and those of the oxygen and the hydrogen

which have given rise to it," says Huxley in Lay Sermons, ("The

Physical Basis of Life"), New York, 1874, p. 136.

204 PHILOSOPHY AND CIVILIZATION

ducible activities and qualities there must be irre-

ducible substances. Of course, the scholastics were

unable to observe, as we can, the chemical activities

of corporeal bodies. But this is simply a matter of

application and the principle remains. The sub-

stance of hydrogen is quite different from that of

water; this is what I have called the specificity of

objects. A corporeal substance cannot be more nor

less than what it is. Water is plainly water

or it is something quite different; it cannot have

degrees of being water. Just as a person cannot

be more or less man than another man. ''Essentia

non suscipit plus vel minus." Accordingly, the

world offers the greatest diversity of irreducible

substantial perfections.

But let us consider more closely this phenome-

non of basic change, from one substance into an-

other or into several other substances, — for in-

stance, water becoming hydrogen and oxygen. If

Thomas had been invited to interpret this phenome-

non, he would have said: that the substance of the

water transformed itself into 7ie'w substances, hy-

drogen and oxygen, and that the hydrogen was in

the water potentially, or in promise. But then, he

would add, every substance that comes into being

consists at bottom of two constituent elements; on

the one liand, there must be something common to

the old state and to the new, and on the other hand

there must be a specific principle. That which is

common to the two stages of the process is an in-