It is not difficult to program a computer to give it the appearance of understanding English and producing intelligent responses. One simple method is to match a series of words against a pattern (which is like a partly specified sentence) and, if the words match, to give a predefined response. The technique can be made a little more powerful by including some of the original words in the response. This, and a few other tricks, were used in ELIZA, which was celebrated as an early computer program that could hold an extended dialogue with a human being. But its facade crumbles when you ask it a question with a complicated grammatical structure, or one that demands a reasoned or calculated response. What ELIZA lacks is firstly a means of recognizing the grammatical structure of language and secondly a means of converting the user's query into a represention of the underlying knowledge, from which inferences can be drawn. Despite its limitations the ELIZA approach of word pattern matching has some use as a simple means of communicating with a computer through natural language, in circumstances where `user-friendliness' is more important than precision.