Topic 21: Inductive Argument

Of the three major kinds of arguments commonly distinguished by logicians – the deductive, inductive and abductive – inductive arguments are probably the most common and useful.

An inductive argument is an argument in which there is some kind of

extension or generalization from a situation (a ‘source’) to some wider

or related situation (a ‘target’).

For example, suppose you have been given a box of chocolates, each wrapped in the same brown shiny foil. You open and eat two of them, and find that they both have a caramel syrup filling. If you conclude that all chocolates in the box have caramel filling, then you would have made an inductive inference, generalizing from the sampled chocolates to the whole ‘population’ of chocolates in the box.

Inductive Generalizations

Inductive arguments of this kind (from samples to whole populations) are known as inductive generalizations. You will be familiar with them because they get reported in the news all the time. When you hear that 87% of US citizens do not know the difference between a Sunni and a Shiite, you are hearing an inductive generalization from a sample of maybe 300 folks in places like Iowa and Ohio to their 300 million compatriots.

Inductive arguments rely on there being detectable patterns in the world. In making an inductive inference you are hoping that a new situation will be a continuation of the pattern you have seen already. If you are lucky or wise, you have identified a pattern that really does hold up.

Statistical Syllogism

An inductive argument can be driven in the other direction, from the general to the particular. Suppose you have succumbed to temptation and eaten 10 chocolates from the box; they have all had caramel fillings. You reach out for another, telling yourself that this chocolate will definitely be the last one. If you are expecting caramel again, you are expecting this particular final chocolate to continue the pattern of the previous 10. This kind of inductive inference from a more general claim to a particular case is known as a statistical syllogism.

Analogy

A third common kind of inductive argument is the use of analogy. An analogical argument picks up on the similarity between two particular situations, and extends knowledge from one to the other. For example, suppose you have eaten one chocolate with a brown silvery foil and it had a caramel filling. You pick up another, and before unwrapping it, you think

‘This chocolate seems just like the one I just ate. It probably has a caramel filling too.’ Probably unwittingly, you would have made an analogical inference.

Arguments by analogy can, of course, be much more serious. The similarities between the US interventions in Vietnam and Iraq have often been noted. One might argue that, since the Vietnam war ended in a humiliating US withdrawal, and the Iraq war is just like the Vietnam war, the US will make a humiliating withdrawal from Iraq too.

Figure 2.23

Inductive arguments, like any other arguments, can be laid out in an argument diagram or map. When these arguments are made fully explicit, there will always be a premise of some kind asserting the similarity between the source situation and the target situation.

Inductive arguments are always at risk of misfiring. This happens when reality fails to conform to the pattern we think we have identified. For centuries, Europeans believed that all swans were white, making a reasonable inductive generalization from the swans in their experience. As they later found out, when black swans were found in Australia, their generalization had been confounded by nature, whose real patterns are endlessly subtle and diverse.

How can you tell how strong an inductive argument is? There is no general answer to this, but there is, fortunately, a sophisticated science of inductive reasoning. You can begin to learn this science by studying disciplines such as probability, statistics, and scientific method.