What you use throughout the process of writing, and especially in the prewriting and revising steps, is your mental capacity. Your written expression originates from your thoughts. You have ideas, you build on them, you think of good words, form sentences, express your views and give your writing a structure and a flow. Apart from planning and organizing your thoughts and putting them in the right words, you also use figurative language, you play with words, and you may use imagery to add to the impact of the writing. This requires you to visualize and imagine. Initially, you have abstract ideas. You build on and extend some of them, discard others, and give your ideas a concrete form. This requires the use of your imagination, vocabulary, and other language skills. You need to analyze and even criticize your own thoughts, and improve on them before putting them in the written form. Thus, writing involves the use of research, memory, and analytical skills. Simply put, you use your mind to word your thoughts and express yourself in an effective way. Depending on the kind of writing, you may use various mental faculties as required. A persuasive essay, for example, will require the use of your convincing abilities in writing, a true story will require recalling incidents and organizing them in the right order, while a comedy will require you to use humor or sarcasm.