The Next Logical Step Fallacy

At Amazon I worked with a very smart man called Brent. He ran the Similarities team in Personalization – the ‘Customers who bought this item also bought…’ and the ‘Frequently Bought Together’ parts. They are important pieces of the detail page, showing up above the fold. If you’ve looked at any item on Amazon, you would have seen Sims.




Everyone now and then, someone would have a review with the CEO and then use that as a hammer to get their requests forced onto other teams. They would come up to Brent and say, “We need to put X up high on the detail page because Bezos said so.”

His answer would be, “Show me where Bezos said to reduce revenues by moving Similarities.”

This was a great answer. It points out that when someone says to do X, there are a whole lot of unspoken caveats – those are supposed to guide teams, not be used as direct orders. It says I’m going to look at what the original speaker wanted, not at what you want. It says use your brain. It says the Prison Guard Defense (“I was just following orders.”) doesn’t work.

I was reminded of this when I read this blog post on Velvet Glove, Iron Fist:

It may be fallacious to claim that because we are forced to wear seat-belts, we should be forced not to smoke or eat fatty foods, but campaigners who call it ‘the next logical step’ are not wholly wrong. Those who opposed seat-belt laws in the 1970s did indeed warn of a slippery slope and, what’s more, they turned out to be right. One needs to look no further than ‘Healthy Nudges’ to see the truth of this. It refers to seat-belts no fewer than six times in eight pages. The message is clear—it was for your own good then and it’s for your own good now.

[… see link to read context from Nudge]

Did politicians of the 1970s intend compulsory seat-belts to be used as a precedent for smoking bans and tax rises? Surely not. Would they have passed the legislation had they known what it would lead to? Probably not. Saying ‘we did that therefore we must do this’ might be fallacious, but people are susceptible to fallacious arguments. Since Nudge revolves around the idea that human beings are fallible, this point could have been more thoroughly explored.

In this case you have a situation that says “Because they made seatbelts compulsory we need to ban smoking in cars.” Brent’s answer would have been, “Show me in the seatbelt law where it says you can extend it to cigarette smoking.”


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