First Order Logic

All objects described are fixed or unique

"John is a student" student(john)

Here John refers to one unique person.

First order predicate logic

Objects described can be unique or variables to stand for a unique object

"All students are poor"

ForAll(S) [student(S) -> poor(S)]

Here S can be replaced by many different unique students. This makes programs much more compact:

eg. ForAll(A,B)[brother(A,B) -> brother (B,A)] replaces half the possible statements about brothers

• Temporal

Represents truth over time.

• Modal

Represents doubt

• Higher order logics

Allows variable to represent many relations between objects

• Non-monotonic

Represents defaults

Propositional is one of the simplest systems of logic.

Propositional Logic

In propositional logic (PL) an user defines a set of propositional symbols, like P and Q.

User defines the semantics of each of these symbols. For example,

o P means "It is hot"

o Q means "It is humid"

o R means "It is raining"