Necessary but not sufficient

Jim Tucker and Sir Humphrey in Yes Priminister

There is a great episode of Yes Prime Minister where Jim Tucker thinks he’s solved a difficult international diplomatic problem and Humphrey explains in his normal obsequious tone that Jim’s logic amounts to the same as “all cats have four legs, my dog has four legs. Therefore my dog is a cat”. (He phrases Jim’s original solution as “we must do something, this is something; therefore we must do it”)

Anyone who knows me will find this hard to believe but I studied logic at University. Of those three years this is one of two bits of logic I can remember: the difference between necessary and sufficient conditions (i.e. to be a cat means to have four legs but not the other way round).

Surely no one is stupid enough to make these mistakes in real life. Well do any of these ring a bell?:

  • My Space is really popular, I want my brand to be really popular. Therefore my brand will re-invent MySpace.
  • People love blogs. I want people to love my brand. Time for a brand blog.
  • The forums on Money Saving Expert  are really active and that creates passionate users. I want passionate users, so I should add forums to my site.

Our challenge for today is to nominate a brand-related site which has entered into the spirit of enabling users without wearing the clothes of a digital brand.

5 thoughts on “Necessary but not sufficient”

  1. […] Finding patterns that transfer from one discipline to another always surprises me – although in many ways I don’t know why. Such resonance can be very misleading too, encouraging the false thinking that things are the same because they have the same facets (necessary but not sufficient!). […]

  2. […] and artistic become extremely blurred terms. Of course there is a very old and broken syllogism I’ve mentioned several times before which confuses necessary and sufficient conditions: my house has a roof, your house has a roof, […]

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