It’s likely that the first word ladder puzzles were created by none other than Lewis Carroll (Charles Lutwidge Dodgson), the talented British mathematician, and author of the Alice’s adventures. According to Carroll, he invented them on Christmas Day in 1877.
A word ladder puzzle consists of two end-cap words, and the goal is to derive a series of chain words that change one word to the other. At each stage, adjacent words on the ladder differ by the substitution of just one letter. Each chain word (or rung of the word ladder), also needs to be a valid word. Below is an example of turning TABLE into CROWN (this time, in nine steps):
TABLE → CABLE → CARLE → CARLS → CARPS → CORPS → COOPS → CROPS → CROWS → CROWN
In another example, it take four steps to turn WARM into COLD.
WARM → WARD → CARD → CORD → COLD
(As each letter of the two words in the last example is different, this is the minimum possible number of moves; each move changes one of the letters).
Word ladders are also sometimes referred to as doublets, word-links, paragrams, laddergrams or word golf.
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Nice one! Nick Berry does something I’ve often considered doing but never found the time by “solving” word ladders and finding longer chains than might have ever been identified before.