8127/frame/fm

Qualified authority.
One who has undertaken a formal study of the subject
or who has extensive experience with it, has communicated with others on
the topic, and can speak to the majority and minority opinions. To proffer
an opinion on a particular case, one must also have reviewed the evidence
and data relevant to that case, and synthesized an 
independent
conclusion.
Simply criticizing another’s conclusion is insufficient.
Small.
How small does small need to be for the likelihood of untruth to
be ignored? The uncomfortable part of this is that there is no absolute answer
because “small” is necessarily relative. One is always 
comparing
hypotheses
rather than considering any hypothesis in a vacuum solely on its own merits.
We’ve discussed likelihood ratios as a means for comparing hypotheses in
this chapter.
Practical application.
This brings us back around to the idea of subjective
certainty. Although we have beat to death the idea that a hypothesis can only
be disproved, never proved, we also embrace the reality that forensic science
is an applied science whose purpose is to supply facts to the trier of the same.
When we analyze the evidence and reference samples and see no differences,
we conclude from this analysis that the two items could share a common
source. For individualizable evidence, the inference may be so strong that we
believe it to be true, even though we could not prove it with absolute certainty.
We state this conclusion of common singular source as an 
opinion
. Based on
the experience and knowledge of both the forensic community and the indi-
vidual, we may reasonably accept a properly qualified conclusion as fact.
G.
Summary
Charles Sanders Peirce, the founder of the 
Philosophy of Pragmatism
, defined
absolute truth as: “whatever scientists say it is when they come to the end of
their labors” (Horgan, 1996). This is a particularly appealing bit of philoso-
phy for those of us working in the applied sciences, particularly one such as
forensic science where an entirely unrelated discipline depends on us to
provide it with “facts.” Although we govern ourselves by the rules of science,
we also embrace the practical nature of our endeavor. Pragmatism provides
the philosophical foundation for Stoney’s clarification that individualization
cannot be proved, we can only become convinced of it (Stoney, 1991).
However, to become convinced of an individualization, one must first
be convinced that such a possibility exists. This conviction grows from an
understanding of the nature of the evidence, including its inherent possibilities
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Classification, Identification, and Individualization
151
and limitations. This is rarely accomplished by a single person. A communal
effort is needed to produce a body of empirical work that can support that
pragmatic leap of faith to a conclusion of a single common source. In addi-
tion, each practitioner must rely on an individual body of education, training,
and most of all experience, to justify his conclusion of individuality. The
greater the common wisdom and the more extensive the individual experi-
ence, the more confidence we have that the leap of faith is both appropriate
and justified. Equally important are the checks and balances that a working
community provides in helping the individual analyst determine when the
limitations of the evidence or the tests prevent individualization as a reason-
able conclusion in any specific case.
When individualization is not legally necessary, and identification is
sufficient, no further information is required. However, when individualiza-
tion is desirable, but not possible, we default to classification. In this situation,
more than one source could have produced the evidence, and we must
provide an estimate of how many more than one this might be.
Lest we lose sight of why we care, remember that at this point in the
paradigm (Figure 3.1) we are attempting to infer the source of a piece of
evidence. Classification establishes a nonexclusive relationship between some
evidence and its source; individualization establishes a singular relationship
between a piece of evidence and its source. Whether we arrive at a classifi-
cation or an individualization, that information will be used as a link to infer
associations
between objects (for instance, a suspect and the crime scene).
The processes of 
association 
and
 reconstruction
will be the topic of the next
chapter.