Deductive reasoning and logicDeductive reasoning and logic

Making connections

How crime scene analysis worksHow crime scene analysis works

• The first step to crime scene analysis is making observations.

• Observations lead to questions…or…problem statements.

• Example: What crime was committed?

Who committed this crime?

How was this crime committed?

Using logicUsing logic

Logic: a system of reasoning and inferences (conclusions that are based on observations)

• In context of forensics: does the evidence and the description make sense?

• Example: A body was found in an alley. The body had multiple stab wounds but there is very little blood at the crime scene.

• What is one logical explanation/inference of the crime that you can make with this information?

Deductive reasoningDeductive reasoning

Deductive reasoning: A thought process that investigators use to assemble the pieces of a criminal puzzle to reach a logical conclusion.

Looking at factsLooking at facts(AN example of deductive reasoning)(AN example of deductive reasoning)

• Facts: – Ice cream sales go down in the winter– Statistics show that there are fewer instances

of domestic violence in the winter

• Facts:– Ice cream sales go up in the summer– Statistics show that there are more instances

of domestic violence in the summer

What is the logical link?What is the logical link?

• When ice cream sales go up domestic violence goes up.

• When ice cream sales go down domestic violence goes down.

• Conclusion: The more ice cream that is sold, the more domestic violence there will be…the less ice cream sold the less domestic violence

Cause and effectCause and effect

• Describe the cause and effect of ice cream and domestic violence…

• If ice cream sales stop then domestic violence will also stop.

• Do the two really go together?

• While it may seem like the two go together, it does not mean that ice cream sales really effect domestic violence

• What we see when we look at the facts is a relationship that really doesn’t exist because we are only seeing a part of the whole picture…leading to misinterpretation

• What are some other pieces of the puzzle that we haven’t seen yet?

ReasoningReasoning

• False reasoning, as we just saw, can lead to errors and misunderstandings or misinterpretation when evaluating evidence and results.

Sound reasoningSound reasoning

• As experts with a lot of experience, many forensic scientists use a combination of suspicion and reasoning to help solve crimes.

• Using sound reasoning allows for valuable interpretation of evidence while still maintaining objectivity