Peter Mark Roget was an English physician who was born in 1779 and died in 1869. As a hobby he liked to make lists of words and group them together when they were related to one another. Some were related because they were synonyms, such as illegal and unlawful; some because they were antonyms, such as peaceful and warlike; some because they were reminders of one another, such as father and mother. Altogether Mr. Roget made a thousand different groups, or categories, of related words. Every word he knew or could find in the dictionaries that he had was classified in one or more of these categories.