# Artificial Intelligence Reasoning Reasoning Reasoning is the process

• Slides: 14

Artificial Intelligence Reasoning

Reasoning • Reasoning is the process of deriving logical conclusions from given facts. Durkin defines reasoning as ‘the process of working with knowledge, facts and problem solving strategies to draw conclusions’. • Different types of reasoning is as following Ø Deductive reasoning Ø Inductive reasoning Ø Abductive reasoning Ø Analogical reasoning Ø Common-sense reasoning Ø Non-Monotonic reasoning Ø Inference

Deductive Reasoning • Deductive reasoning, as the name implies, is based on deducing new information from logically related known information. A deductive argument offers assertions that lead automatically to a conclusion, e. g. The color of all crows is black, ABC is a crow so its color will be black

Inductive Reasoning • Inductive reasoning is based on forming, or inducing a ‘generalization’ from a limited set of observations, e. g. –Observation: All the crows that I have seen in my life are black. –Conclusion: All crows are black • Thus the essential difference is that inductive reasoning is based on experience while deductive reasoning is based on rules, hence the latter will always be correct.

Abductive reasoning • Deduction is exact in the sense that deductions follow in a logically provable way from the axioms. Abduction is a form of deduction that allows for plausible inference, i. e. the conclusion might be wrong, e. g. Implication: There is no class if It rains. Axiom: There is no class Conclusion: It is raining

Analogical Reasoning • An analogy is a comparison between two objects, or systems of objects, that highlights respects in which they are thought to be similar. Analogical reasoning is any type of thinking that relies upon an analogy. An analogical argument is an explicit representation of a form of analogical reasoning that cites accepted similarities between two systems to support the conclusion that some further similarity exists. In general (but not always), such arguments belong in the category of inductive reasoning, since their conclusions do not follow with certainty but are only supported with varying degrees of strength.

Common-sense and Non-Monotonic reasoning • Common-sense reasoning is an informal form of reasoning that uses rules gained through experience or what we call rules-of-thumb. It operates on heuristic knowledge and heuristic rules. • Non-Monotonic reasoning is used when the facts of the case are likely to change after some time, e. g. Rule: IF the wind blows THEN the curtains sway When the wind stops blowing, the curtains should sway no longer. However, if we use monotonic reasoning, this would not happen. The fact that the curtains are swaying would be retained even after the wind stopped blowing.

Inference • Inference is the process of deriving new information from known information. In the domain of AI, the component of the system that performs inference is called an inference engine.

Rules of inference • Rules of inference are logical rules that you can use to prove certain things. As you look at the rules of inference, try to figure out and convince yourself that the rules are logically sound, by looking at the associated truth tables. The rules we will use for propositional logic are: • Modus Ponens • Modus Tolens • And-Introduction • And-Elimination

Modus ponens • “Modus ponens" means "affirming method“. Note: From now on in our discussion of logic, anything that is written down in a proof is a statement that is true. Modus Ponens says that if you know that alpha implies beta, and you know alpha to be true, you can automatically say that beta is true. A B -Modus Ponens

Modus Tolens • Modus Tolens says that "alpha implies beta" and "not beta" you can conclude "not alpha". In other words, if Alpha implies beta is true and beta is known to be not true, then alpha could not have been true. Had alpha been true, beta would automatically have been true due to the implication.

And-Introduction and-Elimination • And-introduction say that from "Alpha" and from "Beta" you can conclude "Alpha and Beta". That seems pretty obvious, but is a useful tool to know upfront. Conversely, andelimination says that from "Alpha and Beta" you can conclude "Alpha".

Inference Rules