Why a ladder up a tree?

A word ladder is already a climb. You start with one word at the bottom and change a single letter at a time until you reach a different word at the top. Every new word is a rung. We drew that ladder, leaned it against a tree, put a treehouse at the top, and gave you a small critter who climbs one rung for every real word you make.

The ladder starts with exactly as many rungs as the shortest solution needs. Find that route and the critter steps straight into the treehouse. Take a longer way and the ladder grows extra rungs to get you there, so you always finish, but the stars go to the shortest climb. The trees get taller as you go, from three-letter words on the Sapling to five-letter words on the Giant Tree.

A bit of real word ladder history

Lewis Carroll, the author of Alice’s Adventures in Wonderland, came up with this puzzle around Christmas 1877. A rare-book dealer’s description of his rule booklet says he made it for two young ladies who had “nothing to do”, and the booklet is inscribed to Julia and Ethel, the Arnold sisters. His diary first mentions the game on 12 March 1878, when he called it Word-links.

On 29 March 1879 the magazine Vanity Fair began printing his puzzles under a new name, Doublets. Macmillan published them as a small book the same year, with the rules and a long glossary of allowed words. Carroll’s rules are the ones this game uses: two words of the same length, linked by words that each differ from the next by one letter, with every letter keeping its own place. His own example turned HEAD into TAIL through heal, teal, tell and tall. That exact ladder is level 32 here.

The puzzle picked up other names later. Vladimir Nabokov mentioned it as “word golf” in his novel Pale Fire. In 1993 the computer scientist Donald Knuth used 5,757 five-letter words in his book The Stanford GraphBase to study these ladders with a computer.

The three trees

• Sapling, levels 1 to 20: three-letter words, 3 to 5 steps. Level 1 turns CAT into DOG.
• Oak, levels 21 to 40: four-letter words, 4 to 6 steps, including Carroll’s HEAD to TAIL.
• Giant Tree, levels 41 to 60: five-letter words, 5 to 8 steps. The last one turns AMONG into WHALE.

How to play

• Your word sits on the ladder. Tap one of its letters, then tap a new letter on the keys.
• If the new word is a real word, it becomes the next rung and your critter climbs up.
• Reach the word in the treehouse to finish the level. A longer route adds extra rungs.
• On a keyboard, the arrow keys pick a letter, typing changes it, and Backspace undoes a rung.
• Hint shows the next word on a shortest ladder. You get 3 per level.
• Stars: 3 for the fewest steps with no hints, 2 for up to 2 extra steps, 1 for any climb.
• Earn 3 stickers in this game for your QuickBOP sticker book.
• Sound is on to start. Tap 🔊 to mute, or 🎵 for music.

Tips

Compare the two words first. Each step fixes at most one letter, so CAT and DOG, which differ in all three letters, need at least three steps. If the fewest is bigger than the number of different letters, some letter has to change twice.

Watch the vowels. Swapping one vowel for another is usually easy: CAT, COT, CUT. Turning a vowel into a consonant is the hard part, so look for the spot where that can happen.

Work backward. Think of words one letter away from the treehouse word. The last rung is often easier to spot from the top.

Undo is free. Stars only count the rungs on your finished ladder, so climb down and try another branch as often as you like.

Your turn

The Sapling at the top of this page has CAT on the ground and DOG in the treehouse, three steps apart. See if your critter can get there without a hint.