are not so alike in their mode
of operation as to produce results identical in every circumstance.
The expert inquirer knows by previous observation that when gunpowder
acts the objects in the neighbourhood are blackened; and that an
explosion of dynamite tears and shatters in a way peculiar to
itself. He is thus able to interpret the traces, to make and prove a
hypothesis.

A man's body is found dead in water. It may be a question whether
death came by drowning or by previous violence. He may have been
suffocated and afterwards thrown into the water. But the circumstances
will tell the true story. Death by drowning has distinctive symptoms.
If drowning was the cause, water will be found in the stomach and
froth in the trachea.

Thus, though there may be a plurality of possible causes, the
causation in the given case may be brought home to one by distinctive
accompaniments, and it is the business of the scientific inquirer to
study these. What is known as the "ripple-mark" in sandstone surfaces
may be produced in various ways. The most familiar way is by the
action of the tides on the sand of the sea-shore, and the interpreter
who knows this way only would ascribe the marks at once to this
agency. But ripple-marks are produced also by the winds on drifting
sands, by currents of water where no tidal influence is felt, and
in fact by any body of water in a state of oscillation. Is it, then,
impossible to decide between these alternative possibilities of
causation? No: wind-ripples and current-ripples and tidal-ripples have
each their own special character and accompanying conditions, and the
hypothesis of one rather than another may be made good by means of
these. "In rock-formations," Mr. Page says,[1] "there are many things
which at first sight seem similar, and yet on more minute examination,
differences are detected and conditions discovered which render
it impossible that these appearances can have arisen from the same
causation."

The truth is that generally when we speak of plurality of causes, of
alternative possibilities of causation, we are not thinking of
the effect in its individual entirety, but only of some general or
abstract aspect of it. When we say, _e.g._, that death may be produced
by a great many different causes, poison, gunshot wounds, disease of
this or that organ, we are thinking of death in the abstract, not of
the particular case under consideration, which as an individual case,
has charac