# Inference in terms of Artificial Intelligence

In this article, we are going to learn about the meaning of Inference in terms of uncertainty in Artificial Intelligence. We will first define what inference is and will also study the various inference rules that are used by us or the agent while making the conclusions using the inference process.
Submitted by Monika Sharma, on June 11, 2019

Inference means to find a conclusion based on the facts, information, and evidence. In simple words, when we conclude the facts and figures to reach a particular decision, that is called inference. In artificial intelligence, the expert system or any agent performs this task with the help of the inference engine. In the inference engine, the information and facts present in the knowledge base are considered according to the situation and the engine makes the conclusion out of these facts, based on which the further processing and decision making takes place in the agent.

The inference process in an agent takes place according to some rules, which are known as the inference rules or rule of inference. Following are the major types of inference rules that are used:

1) Addition: This inference rule is stated as follows:

```       P
----------
∴P v Q
```

2) Simplification: This inference rule states that:

```     P ^ Q                               P ^ Q
----------                OR        ----------
∴P                                  ∴Q
```

3) Modus Ponens: This is the most widely used inference rule. It states:

```    P->Q
P
-----------
∴Q
```

4) Modus Tollens: This rule states that:

```    P->Q
~Q
-----------
∴~P
```

5) Forward Chaining: It is a type of deductive Inference rule. It states that:

```    P
P->Q
-----------
∴Q
```

6) Backward Chaining: This is also a type of deductive inference rule. This rule states that:

```    P
P->Q
-----------
∴P
```

7) Resolution: In the reasoning by resolution, we are given the goal condition and available facts and statements. Using these facts and statements, we have to decide whether the goal condition is true or not, i.e. is it possible for the agent to reach the goal state or not. We prove this by the method of contradiction. This rule states that:

```    P v Q
~P^R
-----------
∴Q v R
```

8) Hypothetical Syllogism: This rule states the transitive relation between the statements:

```    P->Q
Q->R
-----------
∴P->R
```

9) Disjunctive Syllogism: This rule is stated as follows:

```    P v Q
~P
-----------
∴Q
```