t weight to each of these coefficients. Death may be
the result of a combination of causes; organic disease co-operating
with exposure, over-fatigue co-operating with the enfeeblement of the
system by disease.

The technical names for these difficulties, Plurality of Causes and
Intermixture of Effects, are apt to confuse without some clearing up.
In both kinds of difficulty more causes than one are involved: but
in the one kind of case there is a plurality of possible or equally
probable causes, and we are at a loss to decide which: in the other
kind of case there is a plurality of co-operating causes; the effect
is the result or product of several causes working conjointly, and we
are unable to assign to each its due share.

It is with a view to overcoming these difficulties that Science
endeavours to isolate agencies and ascertain what each is capable of
singly. Mill and Bain treat Plurality of Causes and Intermixture of
Effects in connexion with the Experimental Methods. It is better,
perhaps, to regard them simply as obstacles to explanation, and the
Experimental Methods as methods of overcoming those obstacles. The
whole purpose of the Experimental Methods is to isolate agencies and
effects: unless they can be isolated, the Methods are inapplicable.
In situations where the effects observable may be referred with equal
probability to more than one cause, you cannot eliminate so as to
obtain a single agreement. The Method of Agreement is frustrated. And
an investigator can get no light from mixed effects, unless he
knows enough of the causes at work to be able to apply the Method
of Residues. If he does not, he must simply look out for or devise
instances where the agencies are at work separately, and apply the
principle of Single Difference.

Great, however, as the difficulties are, the theory of Plurality and
Intermixture baldly stated makes them appear greater than they are in
practice. There is a consideration that mitigates the complication,
and renders the task of unravelling it not altogether hopeless. This
is that different causes have distinctive ways of operating, and leave
behind them marks of their presence by which their agency in a given
case may be recognised.

An explosion, for example, occurs. There are several explosive
agencies, capable of causing as much destruction as meets the eye at
the first glance. The agent in the case before us may be gunpowder or
it may be dynamite. But the two agents