What is a word ladder?

The puzzle Lewis Carroll invented on Christmas Day 1877, and what became of it.

Three steps, and each one is a word you could look up. That constraint is the whole puzzle. Without it you could scramble anything into anything.

Who invented word ladders

Lewis Carroll, the author of Alice's Adventures in Wonderland, invented the form at Christmas 1877. He devised it for two young friends, Julia and Ethel Arnold, who had complained of having nothing to do.

He first called the game Word-links, and the earliest mention of it in his diary is 12 March 1878. By the time he published it he had renamed it Doublets, and a series of his puzzles and solutions began appearing in the magazine Vanity Fair from the issue of 29 March 1879. A book followed the same year.

Carroll's own terms are still the neatest description of the puzzle: you are given two words of the same length, and you build a chain of links between them.

The rules of a classic word ladder

1. Start and end words are given, and they are the same length.
2. Change exactly one letter at each step.
3. Do not reorder the letters. Position matters.
4. Every intermediate step must be a real word.
5. The shorter the chain, the better the solution.

That last rule is what makes ladders competitive. Most pairs have many valid chains and only one or two of minimum length.

How to solve one

Work from both ends

Solving forwards from the start word means searching a tree that widens with every step. Working from both ends at once and trying to meet in the middle cuts the search dramatically, because you only need each half to reach a common word.

Fix the letters that already agree

Compare your start and end words position by position. Letters that already match are usually best left alone. If COLD must become WARM, nothing matches, so you know every one of the four positions has to change and the chain is at least four steps.

Move the vowels last

Consonant substitutions tend to leave you with more valid words to move to. Changing a vowel often strands you on a word with no onward step.

Watch for the dead end

Some words are cul-de-sacs. They are real words with no single-letter neighbours at all, so stepping onto one ends the attempt. Backtracking early is cheaper than pushing on.

The growing ladder, a different puzzle

Modern puzzles often use the phrase "word ladder" for something related but distinct: a chain in which each word is one letter longer than the last, rather than the same length with one letter swapped.

This is a genuinely different puzzle and it is worth being clear about why. In Carroll's version the words are linked to each other, each one derived from the one before. In a growing ladder they are not. The words above share nothing except their length and a rule that applies to all of them, in this case that every word starts with S.

That changes what the puzzle asks of you. A Carroll ladder is a search problem: there is a correct chain and you are looking for it. A growing ladder is a recall problem: there are thousands of valid answers at every rung and you need to produce one, quickly, that fits the constraint.

Where Wordascent fits

Wordascent is a growing ladder, not a Doublets puzzle. Seven rungs, three letters up to nine, and a rule every word must follow that changes daily. One puzzle a day, the same for everyone, three minutes on the clock.

If what you want is Carroll's original, this is not that, and you would be better served by a Doublets collection. If you want the recall game, this is it.

Play today's climb

Sources

• Word ladder, Wikipedia, for the 1877 invention, the Word-links name, the 1878 diary entry and the 29 March 1879 Vanity Fair publication.
• Lewis Carroll Resources: Doublets, for Carroll's published puzzles.