Okay, then it's time to learn another language.

Propositional logic, as we've seen, is awkward, at least for the wumpus, for other things

as well.

So I would like to do some language games with you.

What are you seeing here?

This is the important blocks world example.

Think about blocks with different colors and possibly different shapes are put onto a table

which I'm representing by this black line.

If you wanted to describe this picture to somebody, your grandmother, how would you do it?

The experiment here is that I want to understand what kind of language you would use, which

means that you have to actually give me some language.

Could you relate?

I see five red cubes with letters in it from A to A, D, B, E, C, so not ordered, and they

all sit on a black line.

Right, which I think we think of as a table.

Can you say anything else on them, about them?

The gaps between the cubes are not the same length.

Some cubes are nearer to each other than others.

Okay, good.

Usually in the blocks world, this idea is that you have the blocks on a table and then

you have a robot arm that can stack and unstack them and make nice towers and so on.

One of the things that we're always interested in is can I pick them up?

One of the things why I wouldn't be able to pick them up is if I had a block, if I had

a kind of a tower like this, then I cannot pick up C because it's not clear.

So another thing, all of them are clear on top or something like that.

Good.

Thank you, that was excellent.

The thing you've seen here, which you would probably notice more if I've drawn 3,000 red

blocks, is that he didn't talk about the blocks individually.

He said things like all of them are on the table.

Some of them are nearer to each other.

All of them are clear.

All of them are red.

All of them are cubes.

And I had five of them.

That's kind of the language a human uses to understand these things.

We can do this in propositional logic.

We would have kind of propositions of the form A is red, B is red, A is on the table,

B is on the table, A is a block, B is a block, C is a block and so on.

You can imagine if you ever start like this, I'm going to give you 3,000 blocks, a whole

chest of Legos and I'm going to pile them on the table and then you're going to see

... Now, we could do something else.

We could do what he did and say all blocks are red and these kind of things.

Which would be a wonderful description of this, right?

Just the language here and some blocks are nearer to each other than others.

The problem with this is if I know all blocks are red and A is a block, then I would normally

want to conclude that A is red.

But this language, I cannot.

I would have to say something, add knowledge like if all blocks are red and is block A,

then block A, what is it?