Reasoning is the act of using reason to derive a conclusion from certain premises. There are two main methods to reach a conclusion. One is deductive reasoning, in which given true premises, the conclusion must follow (the conclusion cannot be false). This sort of reasoning is non-ampliative - it does not increase one's knowledge base, since the conclusion is self-contained in the premises. A classical example of deductive reasoning are syllogism.

  • 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. A classical example comes from David Hume.

  1. The sun rose to the east every morning
  2. Therefore, the sun will rise to the east 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.

These methods of reasoning are of interest to such disciplines as philosophy, logic, psychology, and artificial intelligence.