An inductive argument is one in which you start from experiences about particular facts and infer general conclusions from it. When we say that all men who are born will die because no one has stopped dying until today, we are using an inductive argument. Such arguments are based on past experience to support a conclusion.
Chalmers, defines an inductive argument as follows:
“If a large number of As were observed under a wide variety of conditions, and if all of these As were observed to have property B without exception, then all As were to have property B. “
Take the boiling point of water as an example. Whenever we watched the water boil (A), it happened at 100 degrees Celsius (property B). So we can conclude that water (A), and any water found on earth or another planet, boils at 100 degrees Celsius (property B).
Induction is generalization
This type of reasoning is also called inductive generalization. The use of the word “generalization” refers to the fact that in an inductive argument “we generalize”, which means moving from particular premises to general conclusions .
Let us consider one more example. Imagine that a group of researchers is developing a medicine to cure AIDS. After being tested on animals and showing promise, the researchers invite a number of AIDS patients to volunteer to test the drug in humans. Initially, five patients agreed to be volunteers. In carrying out the tests, scientists note the following:
Premise 1: Drug R cured patient A’s AIDS.
Premise 2: Drug cured patient B’s AIDS.
Premise 3: Medicine R cured AIDS for patient C.
Premise 4: Medicine R cured AIDS for patient D.
Premise 5: Medicine R cured AIDS of patient E.
Conclusion: The drug R cures AIDS.
Note that the premises are particular: they refer to only one patient who has been cured. The conclusion, on the other hand, is general: when saying that “the medicine R cures AIDS”, it applies to any eventual patient. It means that “every patient who takes medicine R will be cured of AIDS”. Every inductive argument has this characteristic: it starts from particular premises and reaches general conclusions.
Strong and weak inductive argument
The example presented above is a weak generalization. It is a little hasty to conclude that “the drug R cures AIDS” based on just five cases. The ideal would be to do a more in-depth investigation, to test on more patients, in a greater diversity of situations.
An inductive argument can be more or less strong. The strength of an inductive argument depends on the degree of support that the premises provide for the conclusion . Suppose drug R in the previous example has been tested on 10,000 patients around the world and in virtually all cases it has led to the cure of AIDS. Given the number of times the drug has been evaluated, the conclusion that “drug R cures AIDS” is very strong. In other words, the premises being true, the conclusion is unlikely to be false.
Inductive argument with false conclusion
Although it is widely used and fundamental, an inductive argument cannot fully guarantee the truth of the conclusion. Even if the premises are true and the argument is strong, the conclusion may be false.
To illustrate this, let us recall the story of the inductivist turkey, told by Bertrand Russell. He says that in one place there was a turkey who devoted his time to making inductive arguments. After being fed at nine o’clock in the morning, the inductivist turkey began to observe and systematically note the time at which it was fed. He observed that it did not vary, whether it was rain or shine, cold or hot, whether it was a holiday or a weekend, it was always fed at nine in the morning.
After gathering this information carefully, without precipitation, he considered that he could safely conclude the following statement “I will be fed every day at nine in the morning”. And it was with this expectation that on the twenty-fourth of December, Christmas Eve, the turkey was beheaded to serve as food the next day.
The conclusion reached by the inductivist turkey after many observations is legitimate. This is a good inductive argument. However, as an inductive argument does not guarantee the truth of the conclusion even if the premises are true, it turned out to be false, and the turkey had a tragic end.
Chalmers, Alan. O que é a ciência afinal? São Paulo: Brasiliense, 1993.
Walton, Douglas. Informal Logic: A Pragmatic Approach. Cambridge: Cambridge University Press, 2008.