How ELIZA made its replies

You may have watched for a slip: a strange repetition, or a reply that did not quite fit.

ELIZA looked through each message for certain words and sentence patterns. When it found one, it chose a prepared rule and rearranged parts of the person's message into a reply.

If someone mentioned "mother," ELIZA could ask about family. If someone wrote, "My boyfriend made me come here," ELIZA could answer, "Your boyfriend made you come here."

It also had a small memory trick. ELIZA could save a topic and bring it back later.

The replies were assembled from rules. Yet on the screen, they could sound like listening.