re the picture
(as being heavy), the slamming of the door, and the weakness of the
cord: a negative condition was that the picture should have no support
but the cord. When Mill, then, defines the Cause of any event as its
"unconditional" antecedent, he means that it is that group of conditions
(state and process of things) which, without any further condition, is
followed by the event in question: it is the least antecedent that
suffices, positive conditions being present and negative absent.

Whatever item of the antecedent can be left out, then, without affecting
the event, is no part of the cause. Earthquakes have happened in New
Zealand and votes of censure in the House of Commons without a picture's
falling in this room: they were not unconditional antecedents;
something else was needed to bring down a picture. Unconditionality also
distinguishes a true cause from an invariable antecedent that is only a
co-effect: for when day follows night something else happens; the Earth
rotates upon her axis: a flash of gunpowder is not an unconditional
antecedent of a report; the powder must be ignited in a closed chamber.

By common experience, and more precisely by experiment, it is found
possible to select from among the antecedents of an event a certain
number upon which, so far as can be perceived, it is dependent, and to
neglect the rest: to purge the cause of all irrelevant antecedents is
the great art of inductive method. Remote or minute conditions may
indeed modify the event in ways so refined as to escape our notice.
Subject to the limitations of our human faculties, however, we are able
in many cases to secure an unconditional antecedent upon which a certain
event invariably follows. Everybody takes this for granted: if the gas
will not burn, or a gun will not go off, we wonder 'what can be wrong
with it,' that is, what positive condition is wanting, or what negative
one is present. No one now supposes that gunnery depends upon those
"remotest of all causes," the stars, or upon the sun being in
Sagittarius rather than in Aquarius, or that one shoots straightest with
a silver bullet, or after saying the alphabet backwards.

(6) That the Cause of any event is an Immediate Antecedent follows from
its being an unconditional one. For if there are three events, A B C,
causally connected, it is plain that A is not the unconditional
antecedent of C, but requires the further condition of first giving rise
to B. But that