formal than spoken language, which is thought to be casual and conversational. Here, it is believed that children begin to understand that writing serves a purpose. Kroll considers the last phase to be the systematic integration phase. A differentiation and integration between the child's speaking and writing can be seen in this phase. This means that speaking and writing have 'well-articulated forms and functions'; however, they are also integrated in the sense that they use the same system. As a result of the individual being aware of the audience, context and reason they are communicating, both written and spoken language are able to overlap and take several forms at this stage. Kroll used the four phases to give an explanation and generalise about the development of these two aspects of language. The highest significance is placed on the second and third phase, consolidation and differentiation respectively. It could be concluded that children's written and spoken language, in certain respects, become more similar to age, maturation, and experience; however, they are also increasingly different in other respects. The content of the skills are more similar, but the approach used for both writing and speaking are different. When writing and speaking development is looked at more closely it can be seen that certain elements of written and spoken language are differentiating and other elements are integrating, all in the same phase. Perera conducted a survey and her view mirrors that of Kroll to the extent that she used Kroll's four phases. When a child undergoes initial learning of the written language, they have not yet fully mastered the oral language. It is clear that their written language development is aided by their spoken language; it can also be said that their spoken language development is aided by the development of their written language skills. Kantor and Rubin believe that not all individuals successfully move into the final stage of integration. Perera is also aware that it is hard to assign chronological ages to each phase of writing development, because each child is an individual, and also the phases are 'artificial'. 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