# Reasoning

Reasoning is the act of using reason to derive a conclusion from certain premises, using a given methodology. The two most commonly used methods to reach a conclusion are deductive reasoning and inductive reasoning. The specifics of the methods of reasoning are of interest to such disciplines as philosophy, logic, psychology, and artificial intelligence.

## Types of reasoning

In deductive reasoning, given true premises, the conclusion must follow and it cannot be false. This type of reasoning is non-ampliative - it does not increase one's knowledge base - since the conclusion is inherent to the premises. A classical example of deductive reasoning are syllogisms for exmaple:

• all humans are mortal,
• Socrates is a man,
• therefore, Socrates is mortal.

In inductive reasoning, on the other hand, when the premises are true, then the conclusion follows with some degree of probability. This method of reasoning is ampliative, as it gives more information than what was contained in the premises themselves. A classical example comes from David Hume:

• The sun rose to the east every morning up till now,
• therefore the sun will rise to the east also tomorrow.

A third method of reasoning is called abductive reasoning, or inference to the best explanation. This method is more complex in its structure and can involve both inductive and deductive arguments. The main characteristic of abduction is that it is an attempt to favor one conclusion above others by either attempting to falsify alternative explanations, or showing the likelihood of the favored conclusion given a set of more or less disputable assumptions.

A fourth method of reasoning is analogy. Reasoning by analogy goes from a particular to another particular. The conclusion of an analogy is only plausible. Analogical reasoning is very frequent in common sense, science, philosophy and the humanities, but sometimes it is accepted only as an auxiliary method. On inferences by analogy, see Juthe, 2005.