hat we can fathom such cause, noumenally considered, is not to be
supposed. To do this would be to solve that ultimate mystery which must
ever transcend human intelligence. But it still may be possible for us
to reduce the law of all Progress, above established, from the condition
of an empirical generalisation, to the condition of a rational
generalisation. Just as it was possible to interpret Kepler's laws as
necessary consequences of the law of gravitation; so it may be possible
to interpret this law of Progress, in its multiform manifestations, as
the necessary consequence of some similarly universal principle. As
gravitation was assignable as the _cause_ of each of the groups of
phenomena which Kepler formulated; so may some equally simple attribute
of things be assignable as the cause of each of the groups of phenomena
formulated in the foregoing pages. We may be able to affiliate all these
varied and complex evolutions of the homogeneous into the heterogeneous,
upon certain simple facts of immediate experience, which, in virtue of
endless repetition, we regard as necessary.

The probability of a common cause, and the possibility of formulating
it, being granted, it will be well, before going further, to consider
what must be the general characteristics of such cause, and in what
direction we ought to look for it. We can with certainty predict that it
has a high degree of generality; seeing that it is common to such
infinitely varied phenomena: just in proportion to the universality of
its application must be the abstractness of its character. We need not
expect to see in it an obvious solution of this or that form of
Progress; because it equally refers to forms of Progress bearing little
apparent resemblance to them: its association with multiform orders of
facts, involves its dissociation from any particular order of facts.
Being that which determines Progress of every kind--astronomic,
geologic, organic, ethnologic, social, economic, artistic, etc.--it must
be concerned with some fundamental attribute possessed in common by
these; and must be expressible in terms of this fundamental attribute.
The only obvious respect in which all kinds of Progress are alike, is,
that they are modes of _change_; and hence, in some characteristic of
changes in general, the desired solution will probably be found. We may
suspect _a priori_ that in some law of change lies the explanation of
this universal transformation of the homo