Saturday, April 17, 2010
The Power of a Cumulative Case- Part 1
Many times an investigator has an idea that he wants to verify, or just see if it is correct. Other times, the investigator has no idea what happened, but something that he stumbled upon makes him want to learn more. It is quite important that an investigator recognize that (s)he is not objective and be willing to go where his acquired evidence is leading. For example, a crime scene investigator should not go to a crime scene already convinced that the crime was not a murder. This a priori (prior to evidence) conclusion may stifle the investigation (and conviction of a suspect) if the crime was, in fact, a murder. If the evidence points to a murder, and the investigator rejects that hypothesis, they may stall the investigation until some other explanation is available to him(her) to explain the evidence. This is not allowed in crime scene investigations because law enforcement has records upon records of cases that the current case may be compared to. If the evidence is similar, it is valid to rule the crime to be a murder. Then the search for a suspect may begin.
No single piece of evidence may be used to build a case or conclude the type of crime. Not very often does a single piece of evidence point to the possibility of only a single type of crime. When that is multiplied by the pieces of evidence, you end up with many possibilities of crimes for each piece. However, investigators look at all the different crimes that each piece of evidence points to and finds the common crime among the pieces of evidence.
This same process is used to determine suspects. In a court of law, the evidence is presented by the prosecution. However, they do not only present a single piece, since a single piece may point to other possibilities of crimes or suspects. The prosecutors present a "cumulative case" that consists of all the evidence. They also provide a scenario that consistently explains all the evidence.
At this point, the defense is supposed to either show how the evidence is not valid or show how the evidence can be explained consistently by some other crime or suspect (not their's). Sometimes the defense may even attack the prosecution's interpretation of the evidence. In the end, the crime, suspect, and scenario that consistently explain the event are to be held to be true, and a verdict is presented on those grounds.
Part of the "cumulative case" is providing evidence against opposing options. The prosecution may also provide evidence that eliminates specific crimes or suspects from the line that the defense may offer as an alternative possibility. Both positive arguments and evidence (for the prosecution's case) and negative arguments and evidence (against the defense's case) are part of a cumulative case.
Our decision to follow a specific worldview should be no different. Many philosophical and scientific truths have been discovered about the world we live in. We must acknowledge them all and be willing to allow ourselves to be guided by the evidence to a conclusion rather than by our a priori commitments. No one comes to any investigation without some idea (completely objective). We need to not deceive ourselves into thinking that we are completely objective, and humbly recognize our biases enough that if the evidence points us another direction, we follow it.
As I mentioned, anyone who is defending their worldview must provide both positive and negative arguments. Many people believe that they can turn someone to their worldview by the process of elimination (only negative arguments, no positive ones). If the person is already convinced against a specific worldview, they tend to assume the position of ignorance rather than accept the worldview they are convinced is wrong. However, other people only provide positive arguments. It does not do much good to only show that your worldview can account for all the evidence...the other person may also be able to do that- giving them no reason to accept yours over theirs. Both positive and negative arguments and evidences must be provided. Positive for why your worldview should be accepted, and negative for why another worldview should be rejected. In isolation from one another, the positive and negative arguments and evidences may only get people as far as taking an agnostic position. In tandem, however, they provide a path to successfully transition from one worldview to another.
This week, I've talked about the importance of having a cumulative case for a worldview. Next week, I will talk about the power of a cumulative case from a psychological perspective.