Necessary and Sufficient

by Krishna on April 22, 2011

A useful nonsense detector method for assessing the quality of someone’s argument is to use the “Necessary and Sufficient” Test. Let us say someone makes an assertion, “If X is done, then Y will happen”. There are two questions to ask here:

  • Is it Necessary?: “If X is *not* done, will Y *not* happen?” (i.e., is X necessary for the occurrence of Y?)
  • Is it Sufficient?: “If X is the *only thing* that is done, then will Y happen?” (i.e., is X sufficient for the occurrence of Y?)

This is not to put someone on the spot, but if you get an honest answer, what you tend to see is the assertion morphing to, “If X is done, then there is a greater likelihood that Y will happen, all other things remaining the same.

The “all other things remaining the same” is a bigger qualifier than it seems. Because when X is done, other things don’t remain the same. For example, if you are spending a lot of money to advertise your product in Canada, there is a likelihood that your product will sell more in Canada. But when you do that, it is also possible that your competitor notices what you are doing and also invests a ton of cash in outspending you in ads, and even comes up with a funny ad mocking your product.

A fantastic example of this was Coca Cola versus Pepsi ads in India in 1996. Coca Cola purchased the advertising rights for the “official drink” of the 1996 Cricket World Cup being held in India. When they started their ad campaign, Pepsi came out with a remarkable series of popular ads stating “Nothing official about it”, effectively killing any gains made by Coca Cola.

In the real world, every action has consequences beyond its immediate result. The lesson is not to stop trying, but to understand what those consequences would be.

I recently read some letters in a paper where, as usual, people were complaining about that teachers were being overpaid, they could not be fired easily and the quality of teaching was poor. But what if you gave these people exactly what they asked for?

If you could fire teachers easily, they would demand greater salaries and severance pay for the risk involved in taking a teaching job. In addition, junior teachers would ask for greater pay because there is no chance of becoming “permanent”. The pension model would become unworkable/useless and again salaries would go up.

If you reduce the salaries of teachers, then fewer people would go into the profession. Definitely students today have a choice of very high-paying jobs in finance and technology. There may be those who are genuinely interested in teaching, but interest does not equal competency. All this is not helping the quality of education.

This is not to say that nothing can be done to improve the education system or manage teachers, but people oversimplify what can be done by only considering one action and don’t think through all the ramifications. They also expect many good results to come from one action and ignore the bad results.

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