be tested--therefore the individual conditions--i.e.: the individual
sources of evidence have to be established and their values
to be determined and _*varied_. Finally, the accompanying change in
effect (conviction by evidence) is to be tested. The last procedure
requires discussion; the rest is self evident. In our business isolation
is comparatively easy, inasmuch as any individual statement, any
visual impression, any effect, etc., may be abstracted without difficulty.
Much harder is the determination of its value. If, however,
we clearly recognize that it is necessary to express the exact value
of each particular source of evidence, and that the task is only to
determine comparative valuation, the possibility of such a thing, in
at least a sufficiently close degree of certainty, must be granted.
The valuation must be made in respect of two things--(1) its
_*reliability_ (subjective and relative); (2) its _*significance_ (objective and
absolute). On the one hand, the value of the evidence itself must
be tested according to the appraisement of the person who presents
it and of the conditions under which he is important; on the other,
what influence evidence accepted as reliable can exercise upon the
_*effect_, considered in and for itself. So then, when a testimony is
being considered, it must first be determined whether the witness
was able and willing to speak the truth, and further, what the importance
of the testimony may be in terms of the changes it may
cause in the _*organization_ of the case.

Of greatest importance and most difficult is the variation of conditions