There are two main types of arguments: deductive and inductive.

Deductive arguments

Deductive arguments are arguments in which the premises (if true) guarantee the truth of the conclusion. The conclusion of a successful deductive argument cannot possibly be false, assuming its premises are true. This is what it means to label an argument as “valid” in logic.  The form or structure of a deductive argument is the essential aspect to consider.

The most famous deductive argument is the aristotelian syllogism:

All men are mortal,
Socrates is a man,
therefore: Socrates is mortal.

 Here another deductive example

1) All dogs are mammals.
2) Buddy is a dog.
SO) Buddy is a mammal.

deductive arguments image

Inductive arguments

Inductive arguments are arguments with premises which make it likely that the conclusion is true but don’t absolutely guarantee its truth.  Inductive arguments are by far the most common type of argument we see in our daily lives. We can assess inductive arguments along a spectrum of successful (stronger) to unsuccessful (weaker). The more successful (stronger) argument is the one in which the premises lead to a conclusion that is probably true, with a high degree of likelihood. It is important to remember that inductive arguments can never fully guarantee the truth of the conclusion.

Premise 1: The bridge X is regularly inspected by qualified engineers.
Premise 2: Vehicles have been driving over it for years.
Conclusion:  It will be safe to drive over it tomorrow.

Inductive arguments are an essential tool for living in a world where we make decisions based on predictions but without absolute certainty. Inductive arguments cannot logically guarantee the truth of a conclusion. If we can’t guarantee truth, the best we can do is use terms like “probable” or “highly likely.” Often, we ignore that in our day-to-day speech and written communication, but it’s a key point to remember.

Inductive arguments can’t guarantee the truth of a conclusion because they’re based on experience, which is always limited.

Inductive arguments move from specific to general. A deductive argument is one that moves from general to specific.

We begin with a general (universal) claim, which happens to be a definition (a dog is a mammal), and we end up with a specific conclusion about an individual dog, Buddy.

With an inductive argument, we start instead with specific pieces of evidence and then we move to a generalization.

The premises of an inductive argument are believed to support the conclusion, but do not ensure it. Thus, the conclusion of an induction is regarded as a hypothesis.

Being able to distinguish between deductive and inductive arguments, and to be aware that no inductive arguments can be logically absolutely true, but at most highly probable, is a first step for the evaluation of an argument.

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Coordinator – Centro per lo Sviluppo Creativo Danilo Dolci – Italy