Other than Kroll's theory, there are four principles on early patterns in writing development discussed by Marie Clay in her book "What Did I Write?". The four principles are recurring principle, the generative principle, the sign principle, and the inventory principle. The recurring principle involves patterns and shapes in English writing that develop throughout writing development. The generative principle incorporates the idea that a writer can create new meanings by organizing units of writing and letters of the alphabet. The sign principle is understanding that the word print also involves paper arrangement and word boundaries. And lastly, the inventory principle is the fact that children have the urge to list and name items that they are familiar with, and because of this they can practice their own writing skills.