person to be biased. For example, the person may have witnessed an accident
and be concerned that the victim obtains compensation.
Detecting Bias
Lawyers arguing a case for a client typically seek to prove or at least suggest
bias by identifying something about the witness the their relationship to the
case that could cause bias. For example, one spouse giving evidence in
support of a case brought by the other spouse has obvious temptations and
inclinations towards bias. This sort of relationship will permit a lawyer to
suggest the possibility of bias based on inference. This would be one of many
factors for the court to take into account when assessing. Of course it is
always possible that there is concrete evidence of bias. In the obvious case
this arises where one person treats another person more favourably or less
favourably than is merited. In these situations the court has actual evidence on
which to find bias that can undermine the evidence of witness.
Assessing Truthfulness
It is possible that a witness how knows or at least believes the truth to be X
will nevertheless deliberately not tell the truth with X. Instead they put forward
Y as the truth. As
will be explained below, one method of assessing
truthfulness involves inductive reasoning. Inductive reasoning has two lines of
analysis. (i) It measures a challenged version of the facts against an alternative
version on the basis that the alternative version represents a more probable
view of the facts since it represents the way things normally occur. (ii) If the
evidence is corroborated by a second witness who is completely independent
of the first, the likelihood that the witnesses are each telling the same lie is so
implausible that it is highly likely that each is telling the truth.
However, attempts can also be made to deploy some form (or some alleged
form) of cognitive science to determine whether a witness is telling the truth.
These involve body language, which in the forensic context is referred to as
demeanour, the polygraph and MRI technology.
Body Language: Demeanour of the Witness
A method for assessing credibility is reliance on the body language,
appearance or demeanour of the witness.
When courts do this they are
invoking a law of cognitive science, typically lacking a scientific basis, about
how people look and behave in the witness box when they are telling the truth
and when they are not telling the truth. This law of cognitive science takes the
following form: “A witness who is/is not telling the truth gives indication X/Y
in their body language”.
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