Computer's are remarkably stupid machines, when compared to the human brain. A phrase that may appear straight forward and obvious to us, "Got a light, mate?" Will confuse any but the most sophisticated conversational computer programs. Why? If we ignore the idea of "common phrases", and limit our selves to syntactical parsing. Then we may start to understand the problems. Perhaps even to sympathise with the computer program trying to respond intelligently.
Referring back to the dreadful phrase, "Have you got a light?". Let us assume this to be a straight forward interrogation asking if you have a source of light. The question is unclear. It may mean do you own a source of light, or it may be asking if you have a source of light in your possession. This lack of clarity is often used in comedy. So there you are, out on a dark night with a friend. You need the use of a torch and so you ask, "Have you got a light?". Your friend owns a torch and so replies quite truthfully, "Yes". Now you are starting to get agitated. You were actually requesting a torch, and so you say "Can I borrow it please?". Another unclear phrase. Your friend being a generous chap, replies "Yes, you can borrow my torch." You still have not received what you wanted, a torch, so you say "Give me your torch please", at last a clear statement. Your friend replies "I can't". And so it goes on until at lat you discover that the torch, which your friend owns, is not in his possession.
We can illustrate this more clearly perhaps with an imaginary repetoir. The scene is a dark, moonless night. You are with a friend standing in a wood. The friend is obviously obtuse. He might even be an android, because the answers he gives to seemingly obvious questions reflect very little comprehension.
you: (Requesting a torch) Have you got a light? friend: Yes. you: Can I borrow it, please? friend: Yes, you can borrow my torch. you: Give me your torch! Please! friend: I can't. you: Why not? friend: Why not what? you: Why can't you give me your torch? friend: Because I haven't got it with me. you: Where is it? friend: Where is what? you: The torch! friend: Which torch? you: The torch I want to borrow. friend: What about the torch you want to borrow? you: Where is your torch? friend: My torch is at home.This is the sort of problem that pursues you when trying to create a conversational computer program. Unlike a human, a computer does not automatically cross reference between current and previous phrases. The simplest example of this the use of the word "it". We use "it" a lot. For example.
"Have you got the book I lent you?"
"Yes"
"Can I have it back please"
You understand that in the last sentence, "Can I have it back please", that the word "it" refers to "the book I lent you".