How to solve a word ladder
A word ladder turns one word into another by changing one letter at a time. Here is a method, tried on three real puzzles from the TOWER archive.
The rule
Every step changes exactly one letter, and every step must be a real word. You cannot add or remove a letter, and you cannot reorder them. WARM to WORM is a step (A becomes O). WARM to WORD is not (two letters change).
Step 1: count the differences
Put the two words side by side and count the positions that differ. WARM and COLD differ in all four, so the ladder needs at least four steps. TOWER's par for that puzzle was exactly 4. When every letter differs and par equals the count, each step must fix one position for good.
Step 2: work from both ends
Do not only push forward from the start. List a few real words that are one letter from the goal. For COLD: CORD, COLT, COLA, GOLD, HOLD, TOLD, BOLD. Then look for a word one letter from the start that gets close to one of those. WARM becomes WORM, and WORM is one letter from WORD, which is one letter from CORD, which is one letter from COLD. The full ladder is WARM, WORM, WORD, CORD, COLD.
Step 3: change a vowel to switch families
Words that differ in a consonant often stay in the same family (WORM, WORD). If you run out of moves, change the vowel. The second puzzle, KIND to MEAN (par 4), goes KIND, MIND, MEND, MEAD, MEAN. MIND to MEND is a vowel change, and it moves you from the -IND family to the -END family, where MEAD and MEAN are close.
Step 4: a sideways step is sometimes right
SLIM to TALL (par 5) goes SLIM, SLID, SAID, SAIL, TAIL, TALL. SLID to SAID looks like it goes nowhere, because it does not copy any letter of TALL. It is the move that makes SAIL and TAIL possible. If you are stuck, a step that is not closer can still be the way through. TOWER tells you whether a step was closer, sideways or farther, so you can learn to spot these.
Step 5: back out of dead ends
Some words have few neighbours. If every word you can reach from a branch is a dead end, go back one step and try a different letter. Write the words down as you go so you do not repeat a branch.
Common mistake
Changing two letters at once. If you want to go from WORM to CORD, that is two changes, so you need WORD between them. Check every step by comparing it to the previous word, letter by letter.
Background: Doublets, the word puzzle Lewis Carroll invented
TOWER: daily word ladder
TOWER is a daily word ladder with a par for every puzzle and a hint if you get stuck.
Play the daily word ladder gameKeep going
Questions
How do you do a word ladder?
Start at the first word and change exactly one letter to make a new real word. Repeat until you reach the last word. You cannot add, remove or rearrange letters.
How does a word ladder work?
Each step is a real word that differs from the one before by a single letter. The best ladders use the fewest steps. That count is called par in TOWER.
Is there only one answer to a word ladder?
Often not. Many pairs have several routes, and a longer route still counts. The shortest route is par.
What is a word ladder also called?
Doublets, the name Lewis Carroll gave it in 1877, or sometimes a word chain.