Case Solved (II)

“Great!” I said. “Who dunnit?”.

“Erica.” Ms D looked smug. “Surprised you haven’t already spotted it.”

“Spotted what?”

“That she got to Arthur’s room before Danny! Look, everyone rushed to Arthur’s room when they heard him scream and arrived in order of distance from his room apart from Erica. Therefore she’s lying, therefore she has something to hide – such as attacking Arthur. QED.”

“QED? I don’t think you are demonstrating anything other than faulty logic.” Tact is alien to me just when I need it most… it’s why I have my own business and work with no-one, it’s not through choice…

“Really?” She dropped my documents back on the table, folded her arms and turned to face me square on. How’s that for non-verbal body language? “So why did Erica get there before Danny?”

“Sorry,” I began. “I know I can come across as arrogant, but that doesn’t mean I am. Usually it’s because I am thinking as I am speaking and things come out of my mouth that really need to be reformatted!” I smiled. No smile back. “Look, the problem is like my seeming arrogantness. Just because I seem arrogant it doesn’t follow that I am. Just because Erica didn’t arrive in the “correct” order doesn’t mean she is lying.”

“Why not?”

“Well, alright, she could be lying. Or everyone else could be lying and she could be the only one telling the truth: they all arrived early and she arrived after them. Or she could have already been in the room – perhaps her and Arthur were an item. Or she could be a faster runner, or wake up quicker. Or – well, you get the idea. The facts you have (Erica arrived quicker) do not result in only one possible outcome (that she is the attacker).”

We analysts need to know a lot about logic. Ms D had suggested that there was a line of deductive reasoning which runs as “given this, then that must be true.” For example, “Given Tinkerbelle is a fairy and that fairies can fly, it must be true that Tinkerbelle can fly.” This only holds if all fairies can always fly. Suppose it is possible that while normally fairies can fly sometimes a wicked witch can put a spell on them and they can’t. Assuming they are still fairies (that is, that losing the ability to fly does not stop them being classed as a fairy) then the example “Given Tinkerbelle is a fairy and that fairies can fly, it must be true that Tinkerbelle can fly.” Is no longer correct. We analysts need to test the assumption (that a fairy who can’t fly is still a fairy) and turn the assumption in to a fact (or recognise the risk we are running the assumption is false and mitigate it). We also treasure and value deductive reasoning as that discovers new facts (if our assumptions are correct) such as the deduced fact that Tinkerbelle can fly.

There is another major class of reasoning called inductive reasoning. Take one fact and generalise it out. For example, “Tinkerbelle is a fairy and Tinkerbelle can fly. Therefore all fairies can fly.” Hopefully you can see that there are many scenarios where the premises would still be true (the premises in this case are “Tinkerbelle is a fairy and Tinkerbelle can fly”) but the conclusion may not be true (“all fairies can fly”). Inductive reasoning results in much weaker conclusions than deductive reasoning, that is they have a much higher risk of being wrong. Trouble is the vast majority of reasoning is inductive – it’s how we humans work.

Worse still – it is horrendously common (especially for analysts!) to confuse inductive reasoning with deductive reasoning and think that you have much stronger case than you do. Analysts need to spot faulty reasoning, turn assumptions in to facts (where they can) and build a strong a case as possible for whatever conclusions they come to.

Ms D had inductively reasoned “Erica arrived out of order of distance from the room” (specific fact) “therefore she is lying about everything” (inductive conclusion) “therefore she is the attacker” (inductive conclusion built on a “fact” arrived at inductively!). Worse still, Ms D thought this was an inevitable conclusion following on from her “facts"! But it does not necessarily follow that because Erica arrived out of order she is lying. Even if it was true she was lying it does not necessarily follow that she is the attacker.

Ms D went on the offensive: “So who did dunnit then?”

“Ah, well, glad you asked that.”