agents,
and their properties are positive conditions of the effect. Thus, the
death of a man who has taken prussic acid is as directly the effect of
the organic properties of the man, i.e. the _patient_, as of the poison,
i.e. the _agent_.

To be a cause, it is not enough that the sequence _has been_ invariable.
Otherwise, night might be called the cause of day; whereas it is not
even a condition of it. Such relations of succession or coexistence, as
the succession of day and night (which Dr. Whewell contrasts as _laws of
phenomena_ with _causes_, though, indeed, the latter also are laws of
phenomena, only more universal ones), result from the coexistence of
real causes. The causes themselves are followed by their effects, not
only invariably, but also _necessarily_, i.e. _unconditionally_, or
subject to none but negative conditions. _This_ is material to the
notion of a cause. But another question is not material, viz. whether
causes _must_ precede, or may, at times, be simultaneous with (they
certainly are never preceded by) their effects. In some, though not in
all cases, the causes do invariably continue _together with_ their
effects, in accordance with the schools' dogma, _Cessante causa, cessat
et effectus_; and the hypothesis that, in such cases, the effects are
produced _afresh_ at each instant by their cause, is only a verbal
explanation. But the question does not affect the theory of causation,
which remains intact, even if (in order to take in cases of simultaneity
of cause and effect) we have to define a cause, as the assemblage of
phenomena, which occurring, some other phenomenon invariably and
unconditionally commences, or has its origin.

There exist certain original natural agents, called permanent causes
(some being objects, e.g. the earth, air, and sun; others, cycles of
events, e.g. the rotation of the earth), which together make up nature.
All other phenomena are immediate or remote effects of these causes.
Consequently, as the state of the universe at one instant is the
consequence of its state at the previous instant, a person (but only if
of more than human powers of calculation, and subject also to the
possibility of the order being changed by a new volition of a supreme
power) might predict the whole future order of the universe, if he knew
the original distribution of all the permanent causes, with the laws of
the succession between each of them and its different mutually
independent effects.