Where the word ladder comes from
At Christmas in 1877, two girls told Lewis Carroll they had nothing to do and asked him for some riddles. He did not have any riddles. He invented a puzzle instead, and people have been playing it ever since.
Carroll wrote the story down himself, in the preface to the little book the puzzle became. Two young ladies, he says, were "smarting under that sorest scourge" of "the having 'nothing to do'", and they "besought me to send them 'some riddles'". What they got was a rule.
The rule, as he wrote it
Carroll set out three conditions, and they are worth reading in his own words because two of them are still exactly our rules and the third is the one we broke.
One letter may be changed in one of the given words, then one letter in the word so obtained, and so on, till we arrive at the other given word.
The letters must not be interchanged among themselves, but each must keep to its own place.
It is de rigueur that the links should be English words, such as might be used in good society.
His own worked example is the one everybody still uses. Turn HEAD into TAIL:
HEAD, heal, teal, tell, tall, TAIL
Five changes, one letter each, and every rung along the way is a word. He called the two ends the doublet and the words in between the links, and he called the finished thing a chain, which is the word we still use.
He was making jokes
This is the part that gets lost when the puzzle turns up in a workbook. Carroll was not setting exercises. He was writing gags, and the pleasure was in the pair rather than in the path.
He asked people to turn PIG into STY. To drive APE into MAN. To make FLOUR into BREAD. To turn POOR into RICH. The chain is a little machine for getting from one word to another, and the joke is that the two words already have something to do with each other before you start. Somebody has to walk the whole ladder from APE to MAN, one letter at a time, and arrive at the punchline having done all the work themselves.
That is a design instinct, and it is a good one. It is why the daily crossings in Morphink are chosen for what the two words mean and not only for how far apart they are.
Word-links, then Doublets
He called it Word-links first. His diary on 12 March 1878 describes it that way, as a game for two players, which is worth noticing: the two-player version is not a later addition somebody bolted on, it was there in the first month.
By the time it was published it had a better name. Carroll took Doublets from the witches in Macbeth, chanting double, double, toil and trouble over the cauldron, which tells you roughly how seriously he wanted it taken. It ran in the magazine Vanity Fair from the issue of 29 March 1879, week after week, with puzzles set and solutions printed and readers writing in. Later that year Macmillan published it as a book, with the rules, a scoring system and a glossary of words you were allowed to use.
A puzzle set for two bored children at Christmas had become a weekly column and then a product inside eighteen months. Word games have always moved like this.
The rule we broke
Read Carroll's second condition again.
The letters must not be interchanged among themselves, but each must keep to its own place.
Each letter keeps its place. Combined with the first condition, that means a Doublet only ever replaces. HEAD and TAIL are both four letters long, every rung between them is four letters long, and the word never changes shape.
Morphink lets you add a letter and take one away. OLD becomes GOLD becomes GOLDS. FOLD becomes OLD. The word breathes.
That sounds like a small extension and it changes the whole feel of the puzzle. Under Carroll's rule you are moving along a fixed row of slots, and the question is always which slot to touch. Once the word can get longer and shorter, the shape of the word is a move too, and the space you are searching opens out enormously. A four-letter word has a few dozen replacements available. Give it add and remove and it has hundreds of neighbours. That is why Morphink can run a clock at all: there is nearly always something there, and the difficulty is finding it in ten seconds rather than finding it at all.
It is also why the game is played on a row of tiles you touch rather than on a line you type. Under three operations you have to say where, and a row of letters you can pull a tile out of says that better than a text box.
The rule we kept without meaning to
The third condition is the one that reads like a period curiosity and turns out to be a real design problem.
Such as might be used in good society.
Carroll is being funny, and he is also drawing a line every word game has had to draw since. Which words count? A dictionary that accepts everything accepts a great deal that nobody wants printed in front of them. A dictionary that accepts only the polite ones refuses a player who typed a perfectly ordinary word.
The answer we came to is that these are two different questions and they get two different answers. There is a set of words the game will accept from you, which is large, because being refused a word you know is the most annoying thing a word game can do to you. And there is a smaller set of words the game will show you unprompted, in a hint or a definition or the chain it draws at the end, which is curated, because the game putting a word in front of a stranger is the game choosing to say it.
Carroll got there in one sentence and a raised eyebrow. It took us rather longer.
Why it lasted
The word ladder is about a century and a half old and it has outlived nearly everything invented alongside it. Its rule fits in one line, it needs no board and no equipment, a child can be taught it in a sentence, and it is genuinely hard.
That combination is rare and it does not survive being improved. Every generation that picks the puzzle up is tempted to add something to it, and the ones that lasted are the ones that did not. Carroll's version needed a scoring system and a glossary and nothing else.
We added exactly two moves in a hundred and forty-nine years, and we think that is enough for the next hundred.
Two girls at Christmas wanted something to do. It is still the best reason to make anything.