What word game did Lewis Carroll invent in 1879?

Lewis Carroll invented the word game Doublets in 1879.

Doublets is now more commonly called a word ladder: players transform one word into another by changing exactly one letter at each step, with every intermediate form remaining a valid word. For example, CAT can become DOG through CAT, COT, DOT, DOG.

Carroll said he invented the game on Christmas Day in 1877, although his diary first records it in March 1878 under the name “Word-links.” He later called the puzzles “Doublets” and published them in Vanity Fair beginning on 29 March 1879. A book collection followed later that year.

The game is sometimes confused with anagrams, palindromes, or cryptograms. Unlike an anagram, Doublets changes letters one position at a time rather than rearranging all the letters at once. Its modern names include word ladder, word golf, and laddergram.