Reasoning in Artificial intelligence

In previous topics, we have learned various ways of knowledge representation in artificial intelligence. Now we will learn the various ways to reason on this knowledge using different logical schemes.

1. Reasoning:

The reasoning is the mental process of deriving logical conclusion and making predictions from available knowledge, facts, and beliefs. Or we can say, “Reasoning is a way to infer facts from existing data.” It is a general process of thinking rationally, to find valid conclusions.

In artificial intelligence, the reasoning is essential so that the machine can also think rationally as a human brain, and can perform like a human.

2. Types of Reasoning

In artificial intelligence, reasoning can be divided into the following categories:

  • Deductive reasoning
  • Inductive reasoning
  • Abductive reasoning
  • Common Sense Reasoning
  • Monotonic Reasoning
  • Non-monotonic Reasoning

Note: Inductive and deductive reasoning are the forms of propositional logic.

2.1. Deductive reasoning:

Deductive reasoning is deducing new information from logically related known information. It is the form of valid reasoning, which means the argument’s conclusion must be true when the premises are true.

Deductive reasoning is a type of propositional logic in AI, and it requires various rules and facts. It is sometimes referred to as top-down reasoning, and contradictory to inductive reasoning.

In deductive reasoning, the truth of the premises guarantees the truth of the conclusion.

Deductive reasoning mostly starts from the general premises to the specific conclusion, which can be explained as below example.


Premise-1: All the human eats veggies

Premise-2: Suresh is human.

Conclusion: Suresh eats veggies.

The general process of deductive reasoning is given below:

Reasoning in Artificial intelligence

2.2. Inductive Reasoning:

Inductive reasoning is a form of reasoning to arrive at a conclusion using limited sets of facts by the process of generalization. It starts with the series of specific facts or data and reaches to a general statement or conclusion.

Inductive reasoning is a type of propositional logic, which is also known as cause-effect reasoning or bottom-up reasoning.

In inductive reasoning, we use historical data or various premises to generate a generic rule, for which premises support the conclusion.

In inductive reasoning, premises provide probable supports to the conclusion, so the truth of premises does not guarantee the truth of the conclusion.


Premise: All of the pigeons we have seen in the zoo are white.

Conclusion: Therefore, we can expect all the pigeons to be white.

Reasoning in Artificial intelligence

2.3. Abductive reasoning:

Abductive reasoning is a form of logical reasoning which starts with single or multiple observations then seeks to find the most likely explanation or conclusion for the observation.

Abductive reasoning is an extension of deductive reasoning, but in abductive reasoning, the premises do not guarantee the conclusion.


Implication: Cricket ground is wet if it is raining

Axiom: Cricket ground is wet.

Conclusion It is raining.

2.4. Common Sense Reasoning

Common sense reasoning is an informal form of reasoning, which can be gained through experiences.

Common Sense reasoning simulates the human ability to make presumptions about events which occurs on every day.

It relies on good judgment rather than exact logic and operates on heuristic knowledge and heuristic rules.


  1. One person can be at one place at a time.
  2. If I put my hand in a fire, then it will burn.

The above two statements are the examples of common sense reasoning which a human mind can easily understand and assume.

2.5. Monotonic Reasoning:

In monotonic reasoning, once the conclusion is taken, then it will remain the same even if we add some other information to existing information in our knowledge base. In monotonic reasoning, adding knowledge does not decrease the set of prepositions that can be derived.

To solve monotonic problems, we can derive the valid conclusion from the available facts only, and it will not be affected by new facts.

Monotonic reasoning is not useful for the real-time systems, as in real time, facts get changed, so we cannot use monotonic reasoning.

Monotonic reasoning is used in conventional reasoning systems, and a logic-based system is monotonic.

Any theorem proving is an example of monotonic reasoning.


  • Earth revolves around the Sun.

It is a true fact, and it cannot be changed even if we add another sentence in knowledge base like, “The moon revolves around the earth” Or “Earth is not round,” etc.

2.5.1. Advantages of Monotonic Reasoning:

  • In monotonic reasoning, each old proof will always remain valid.
  • If we deduce some facts from available facts, then it will remain valid for always.

2.5.2. Disadvantages of Monotonic Reasoning:

  • We cannot represent the real world scenarios using Monotonic reasoning.
  • Hypothesis knowledge cannot be expressed with monotonic reasoning, which means facts should be true.
  • Since we can only derive conclusions from the old proofs, so new knowledge from the real world cannot be added.

2.6. Non-monotonic Reasoning

In Non-monotonic reasoning, some conclusions may be invalidated if we add some more information to our knowledge base.

Logic will be said as non-monotonic if some conclusions can be invalidated by adding more knowledge into our knowledge base.

Non-monotonic reasoning deals with incomplete and uncertain models.

“Human perceptions for various things in daily life, “is a general example of non-monotonic reasoning.

Example: Let suppose the knowledge base contains the following knowledge:

  • Birds can fly
  • Penguins cannot fly
  • Pitty is a bird

So from the above sentences, we can conclude that Pitty can fly.

However, if we add one another sentence into knowledge base “Pitty is a penguin“, which concludes “Pitty cannot fly“, so it invalidates the above conclusion.

2.6.1. Advantages of Non-monotonic reasoning:

  • For real-world systems such as Robot navigation, we can use non-monotonic reasoning.
  • In Non-monotonic reasoning, we can choose probabilistic facts or can make assumptions.

2.6.2. Disadvantages of Non-monotonic Reasoning:

  • In non-monotonic reasoning, the old facts may be invalidated by adding new sentences.
  • It cannot be used for theorem proving.