THINKING TOOLS: CELEBRITY ENDORSEMENTS AND A SALESPERSON’S TRICK

Stephen Law

Thinking Tools is a regular feature that introduces tips and pointers on thinking clearly and rigorously. Here we get to grips with two everyday reasoning errors.

Misusing the argument from authority (a favourite of celebrity advertizers)

Sometimes we’re justified in believing something because an authority on the subject tells us that it is true. If a professor of chemistry warns you not to drop a lump of phosphorus into a sink full of water, I would follow her advice.

      But often such ‘appeals to authority’ are fallacious. Take a look at the following arguments: 
 

I am going to find my perfect partner soon.

How do you know?

I consulted the fortune-telling machine on the pier, and it said so. 
 

Blancmange face packs are an effective beauty treatment.

How do you know?

All the celebrities are using them – Anita Beckenposh, actress and pop star, even advertizes them on TV. 
 

Genetic engineering is always morally wrong: it should never be carried out.

Why do you believe that?

Because Dr Bits told me.

Is Dr Bits an expert in ethics and genetic techniques?

No, he is a professor of mathematics. 
 

I believe that Brand X washes whiter than any other brand.

Why?

Because scientists working for the Brand X corporation say so. 
 

In the first two examples, the ‘authorities’ in question are highly dubious. Why should a celebrity be any better informed about the efficacy of blancmange face packs than anyone else?

      In the third, while Dr Bits really is an authority, he is not an authority on the issue in question. There is no reason to suppose that his opinion on the ethics of genetic engineering is any more reliable than anyone else’s.

      In the fourth example, the authority in question may be biased. To what extent can we trust scientists working for a particular company to give impartial advice about its products?

      When appealing to a supposed ‘authority’, you must be warranted in supposing that they really are an authority on the issue in question, that there aren’t many other authorities on the issue holding an opposing view, that the authority is not significantly biased, and so on. Only then is it sensible to place your trust in the authority in question.

False dilemma (a salesperson’s trick)

It is common to argue like this: 
 

Either A or B

      Not A

      Therefore B 
 

This is often a perfectly acceptable form of argument, as in this case:

Either John has a driving license or else John is not permitted to drive.

John has not got a driving license.

Therefore, John is not permitted to drive. 
 

This argument, on the other hand, is not acceptable: 
 

Either 1 + 1 = 5 or 2 + 2 = 5

It is not true that 1 + 1 = 5

Therefore, 2 + 2 = 5 
 

Why not? Because, unlike in the first argument, the alternatives presented in the either/or premise could both be false. People often construct such arguments without registering that both alternatives might be false, as in this example: 
 

Either we cut welfare or the government goes into the red

We cannot allow the government to go into the red

Therefore we must cut welfare 
 

In this case, there are other options not mentioned, such as to raise taxes. Customers often allow themselves to be railroaded into making bad decisions by a salesperson’s use of false dilemma: 
 

Either you give a substantial donation to the Blue Meanie Cult or you will have an unhappy life.

You don’t want an unhappy life, do you?

So make that donation! 
 

Either you buy the Kawazuki K1000 for great home sound entertainment, or else you make do with second rate rubbish.

Are you really prepared to accept second rate rubbish? I thought not.

So you have no choice, do you? You have to buy the Kawazuki K1000! 
 

When next you are presented with a seemingly unavoidable either/or choice by a salesperson, you might wish to take a step back and ask yourself: are these really the only two alternatives available to me?