this account have been directed to occur as they do occur. For, if we
follow back any sequence of physical causation, we soon find that it
spreads out on all sides into a network of physical relations which are
literally infinite both in space (conditions) and in time (antecedent
causes). Now, even if we suppose that the persistence of force is a
sufficient explanation of the occurrence of the particular sequence
contemplated so far as the exhibition of force is there concerned, we
are thus as far as ever from explaining the _determination_ of this
force into the particular channel through which it flows. It may be
quite true that the resultant is determined as to magnitude and
direction by the components; but what about the magnitude and direction
of the components? If it is said that they in turn were determined by
the outcome of previous systems, how about these systems? And so on till
we spread away into the infinite network already mentioned. Only if we
knew the origin of all series of all such systems could we be in a
position to say that an adequate intelligence might determine beforehand
by calculation the state of any one part of the universe at any given
instant of time. But, as the series are infinite both in number and
extent, this knowledge is clearly out of the question. Moreover, even if
it could be imagined as possible, it could only be so imagined at the
expense of supposing an origin of physical causation in time; and this
amounts to supposing a state of things prior to such causation, and out
of which it arose. But to suppose this is to suppose some extra-physical
source of physical causation; and whether this supposition is made with
reference to a physical event occurring under immediate observation
(miracle), or to a physical event in past time, or to the origin of all
physical events, it is alike incompatible with any theory that seeks to
give a purely physical explanation of the physical universe as a whole.
It is, in short, the old story about a stream not being able to rise
above its source. Physical causation cannot be made to supply its own