Deductive and Inductive Arguments
It is often said that the difference between a deductive and in inductive argument concerns whether or not the argument moves from the specific to the general. In other words, inductive reasoning involves starting with premises about the specific and using them to draw conclusions in the form of general statements. On this view, deductive arguments begin with general statements and conclude with specific ones.
For instance, dictionary.com and masterclass.com and livescience.com make such claims about inductive and deductive reasoning. The problem is that this supposed distinction between deduction and induction is incorrect. Although many deductive arguments move from the general to the specific and many inductive arguments go in the opposite direction, it is false that deduction and induction must take these respective forms of reasoning.
A deductive argument is one in which, if the premises are true, the truth of the conclusion is guaranteed. In other words, the structure of the argument is valid, which means it is impossible for the conclusion to be false if the premises are true. An inductive argument is one in which, if the premises are true, the truth of the conclusion is to some degree probable but not guaranteed. That is, it is possible for the premises to be true and yet the conclusion false.
Now, a deductive argument can move from the specific to the general, and an inductive argument can move from the general to the specific. Consider these examples.
You have a bag of exactly five apples. You inspect each apple one at a time. You confirm that each is red. You then construct the following argument: The first apple of five is red. The second of five is red. The third of five is red. The fourth of five is red. The fifth of five is red. Therefore, all of the apples are red.
There are exactly 100 jelly beans in a jar. You’ve inspected 99 of them, and each is blue. You draw the highly probable though not epistemically certain inductive conclusion that all 100 beans are blue. Then you craft the following argument: All of the beans in the jar are blue. Thus, the 100th bean (the one that I have not yet inspected) is blue.
Argument (1) is deductive and yet involves reasoning from the specific to the general. The truth of the premises guarantees the truth of the conclusion. Argument (2) is inductive, although it involves reasoning from the general to the specific. It is highly likely that the conclusion is true. But the premise of the argument doesn’t guarantee the truth of its conclusion. It is possible that the 100th bean is not blue.