Rob Brooks asks you to take a pop quiz:
When Jack was young, he began inflicting harm on animals. It started with just pulling the wings off flies, but eventually progressed to torturing squirrels and stray cats in his neighbourhood.
As an adult, Jack found that he did not get much thrill from harming animals, so he began hurting people instead. He has killed 5 homeless people that he abducted from poor neighbourhoods in his home city. Their dismembered bodies are currently buried in his basement.
Now, knowing what I have just told you about Jack, is it more probable that Jack is: A) A teacher. Or B) A teacher who does not believe in God?
The answer is of course A. It has nothing to do with the merits of being a teacher or an atheist or any of the particulars of the case. It is purely a matter of probability. If you have two sets of events consisting of one set A and another set B that is a subset of A, then B is always less likely than A because if you belong to the set B then you automatically belong to the set A but not vice versa.
But some people may reason in a different way because of what is known as the conjunction fallacy. They start out by viewing the act in moral terms and if they think that atheists are less moral or are amoral, then they may be drawn to choose option B, seeing the information about teachers being common to both cases and thus irrelevant. In fact, if you add an option C that says “A teacher who does not believe in God and also poisons stray animals”, people may think that is even more likely since it adds weight to the moral argument.
Daniel Kahneman in his excellent book Thinking Fast and Slow that I discussed back in 2012 uses many examples like this to illustrate the difference between System I thinking and System 2 thinking. “System 1 operates automatically and quickly, with little or no effort and no sense of voluntary control” while “System 2 allocates attention to the effortful mental activities that demand it, including complex computations. The operations of System 2 are often associated with the subjective experience of agency, choice, and concentration.” (p. 20)
The trouble is that we System 1 always kicks into action first because it is easy and automatic but it can lead us astray. It takes practice to rein it in and give time for System 2 to kick in before making a judgment.