A key concept within SFL is the idea of ‘system’ (hence Systemic). Language as semiotic, the ability to create meaning, is the result of interconnecting systems at different levels of stratification – context, semantics, lexico-grammar, phonology/graphology. A text is an ‘instance’ of language (product) that is made possible from language as a system (potential). The system-potential of language is therefore instantiated in the form of a text-product. On the other hand, however, the system is not a closed one. As the text unfolds through time (process) it also adds to, and affects, the system. System and text are not, therefore, separable but opposite ends of a cline. Halliday uses the analogy of climate (system) and weather (text).