Deductive argument


A deductive argument is one in which the conclusion has been constructed from more general premises.

The deductive argument is generated when we go from the general to the particular. In it, new knowledge is not generated, but positions that were previously known are reinforced. And this, because the information is already in the premises. When moving from the general to the concrete, you first have to identify general laws, theories, or facts, and, following a series of steps, you specify until the most particular conclusion is drawn.

The main strength of this reasoning is that the relationship between the premises and the conclusion is very strong. Since the conclusion drawn strictly derives from what is stated through these premises.

Be very careful with the arguments extracted using this technique. Due to the strength that exists between the conclusion and the premises, conclusions that are not true can be taken for granted, and we are faced with some exceptions. Or, in the same way, that there are premises that we have not considered. We can also be faced with paradoxical facts, giving rise to fallacies.

What is the deductive fallacy?

As we have just mentioned, deductive fallacies can occur due to paradoxical situations. Let's see it through an example:

  • Premise 1: If taxes are raised, more money is raised.
  • Premise 2: Country X has raised taxes.
  • Conclusion: Country X is raising more money.

This reasoning may be fallacious (or not). If the tax increases are so high that they reduce the attraction of foreign capital and the proliferation of businesses, that is, investment; and, furthermore, it discourages consumption, country X may be raising less money. Thus giving rise to a paradoxical situation.

Structure of the deductive argument

To build a deductive argument we need to follow the following steps:

  1. Find general laws or guidelines regarding the topic we want to argue.
  2. From what was mentioned in the previous step, we build the premises we need. These will be based on generalities, and each of them should be more specific than the previous one (in case there are a good number of them).
  3. We obtain the conclusion based on the deduction process that we have carried out from the premises. There needs to be a strict consistent correlation in the information given in all steps. The conclusion must not contradict any of the premises.

Deductive argument example

Next, we are going to show some examples so that, step by step, we can observe that relationship of strength that exists between the premises and the conclusion.

Example A:

  • Premise 1: Trees have branches.
  • Premise 2: The apple tree is a tree.
  • Conclusion: The apple tree has branches.

Analyzing this simple example, we see that the steps that we mentioned as necessary for its construction are fulfilled. The first premise tells us the most general idea: the starting point. The second gives us a little more concrete insight into the idea conveyed by the second premise. And finally, the conclusion follows from the premises and does not contradict them: If the trees have branches and the apple tree is a tree, it is strictly logical and natural to say that the apple tree has branches.

We also see what we said at the beginning. For the deductive argument does not offer information, but rather reinforces what the premises contain. Since we knew that the apple tree was a tree and that trees have branches.

Example B:

  • Premise 1: People in prison have committed a crime.
  • Premise 2: Carlos is in prison.
  • Conclusion: Carlos is a criminal.

The relationship between conclusion and premises is very strong, since, except for judicial error, all people who are in jail are in jail for committing a crime. Thus, if Carlos is in prison, it is because he has committed a crime.

Differences between deductive argument and inductive argument

The deductive and inductive arguments have two fundamental differences.

On the one hand, the way they are built. In the deductive one goes from the general to the particular. Meanwhile, in the inductive, through the fulfillment of certain particularities, a general conclusion is built.

On the other hand, the deductive does not provide us with new knowledge, but rather reinforces the content of the premises. On the other hand, the inductive does provide us with new information.

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