Knowledge Representation and Reasoning Logics for Articial Intelligence

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Introduction
Propositional logics conceptualize domains at, but not below, the level of propositions.
A proposition is an expression in some language
 that is true or false,
 whose negation makes sense,
 that can be believed or not,
 whose negation can be believed or not,
 that can be put in the frame
“I believe that it is not the case that .”
Some examples of propositions are
 Betty is the driver of the car.
 GeorgeW. Bush is sitting down or standing up.
 If Opus is a penguin, then Opus doesn't y.

Need for a Representation Language
Although you can understand and reason about information expressed in natural language,
it is clear that you don't do that by just remembering the sentences you read.
This was demonstrated by Bransford and Franks in a series of experiments reported
in 1971 (Bransford and Franks, 1971). Participants were shown a series of sentences,
including these:
The sweet jelly was on the kitchen table.
The ants in the kitchen ate the jelly.
The ants ate the sweet jelly that was on the table.
The sweet jelly was on the table.
The jelly was on the table.
The ants ate the jelly.


Logic
In the late 1800s and early 1900s, various formal systems were developed by people
who hoped, thereby, to turn human reasoning into a kind of calculation. From our
perspective, we can now see that what these people were engaged in was research in
knowledge representation. The formal systems they developed were systems of logic,
a topic which has been studied since the days of Plato and Aristotle.