How did Dr. Seuss write The Cat in the Hat using a limited vocabulary list?

To write The Cat in the Hat, Dr. Seuss (Theodor Geisel) responded to a 1954 Life magazine article by John Hersey, which criticized existing reading primers for being boring and spiritless.1

In response, William Spaulding of Houghton Mifflin provided Geisel with a specific vocabulary list of fewer than 240 words intended for six- and seven-year-olds. Geisel found the process of working within these constraints to be "painful," noting the difficulty of writing without the use of many adjectives or nouns.1

To overcome the limitation, Geisel focused on finding two rhyming words from the list, which ultimately inspired both the title and the subject of the book. By utilizing these simple words within a structure of rollicking and repetitive rhyme, he created a work that served as a successful alternative to traditional, literal primers.1