Types of induction

5.9 Analogies and evaluating analogies

Analogies proceed from a premise about two things being similar in one respect to a conclusion about their being similar in another respect. One of the most famous analogies of all time is William Paley’s analogy between pocket watches and the universe:

‘Suppose I found a watch upon the ground, and it should be inquired how the watch happened to be in that place, I should hardly think...that, for anything I knew, the watch might have always been there. Yet why should not this answer serve for the watch as well as for a] stone [that happened to be lying on the ground]?... For this reason, and for no other; namely, that, if the different parts had been differently shaped from what they are, if a different size from what they are, or placed after any other manner, or in any order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it'
William Paley, Natural Theology: Or Evidences of the Existence and Attributes of the Deity Collected from the Appearances of Nature (Boston: Gould and Lincoln, 1867)
Image of an Elgin pocket watch

Elgin pocket watch

Licensed by timlewisnm under the Creative Commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0) licence

Paley believes that just as we would never imagine that a pocket watch didn’t have a maker, so we shouldn’t imagine the universe lacks a maker, because both pocket watches and the universe are too complex to have come about by accident.

Here are the questions that, according to chapter 4 of the set text, should be asked to evaluate analogies:

  1. From which property (or properties) are we being asked to extrapolate?
  2. To which property (or properties) are we being asked to extrapolate?
  3. Are the properties from which we are being asked to extrapolate relevant to the properties to which we are being asked to extrapolate?
  4. Are there are any significant differences to be taken into account (in what we are extrapolating from, or in what we are extrapolating to)?

Individual activity: Analysing Hoover’s bad analogy

In 1992 the marketing people at Hoover reasoned that because the take-up of air tickets to Europe on a recent promotion had been low, a promotion offering air tickets to the US in exchange for buying £100 worth of Hoover products would also be low. They were wrong.

Hoover’s inability to recognise a bad analogy cost them £50 million. Check out a report of this fiasco on the BBC news website.

Please evaluate Hoover’s analogy in the light of the four questions above before looking at my answer.

Image of the underside of a small twin-engined jet airplane in flight against a bright blue sky

Licensed by Andrew Malone under the Creative Commons Attribution- 2.0 Generic (CC BY 2.0) licence

  1. Hoover was extrapolating from an offer of tickets to European destinations.
  2. Hoover was extrapolating to an offer of tickets to the USA.
  3. Both are an offer of tickets in exchange for buying Hoover products.

Tickets to the USA (from Britain) are far more expensive than tickets to European destinations (and there is no realistic alternative to flying for a short break). Tickets to the USA cost more than the products customers were being asked to buy to qualify for the tickets.