generation, growth, and their dissolution, which we call their death, we
observe a regular sequence of phenomena, which within the limits of
experience present and past, so far as we know the past, is fixed and
invariable. But if this is not so, if the order and sequence of
phenomena, as known to us, are subject to change in the course of an
infinite progression,--and such change is conceivable,--we have not
discovered, nor shall we ever discover, the whole of the order and
sequence of phenomena, in which sequence there may be involved according
to its very nature, that is, according to its fixed order, some
variation of what we now call the Order or Nature of Things. It is also
conceivable that such changes have taken place,--changes in the order of
things, as we are compelled by the imperfection of language to call
them, but which are no changes; and further it is certain that our
knowledge of the true sequence of all actual phenomena, as for instance
the phenomena of generation, growth, and dissolution, is and ever must
be imperfect.

We do not fare much better when we speak of Causes and Effects than when
we speak of Nature. For the practical purposes of life we may use the
terms cause and effect conveniently, and we may fix a distinct meaning
to them, distinct enough at least to prevent all misunderstanding. But
the case is different when we speak of causes and effects as of Things.
All that we know is phenomena, as the Greeks called them, or appearances
which follow one another in a regular order, as we conceive it, so that
if some one phenomenon should fail in the series, we conceive that there
must either be an interruption of the series, or that something else
will appear after the phenomenon which has failed to appear, and will
occupy the vacant place; and so the series in its progression may be
modified or totally changed. Cause and effect then mean nothing in the
sequence of natural phenomena beyond what I have said; and the real