对学生来说 ,命题作文最让他们感到困难的是如何进行构思。因为它是在一个人大脑内部进行的暗箱操作 ,看不见摸不着 ,所以常常也让老师们觉得神秘莫测、无从下手。所谓命题作文的构思 ,其实就是在人的大脑内部 ,根据表达需要或目的的外化形式———文字符号的编码（命题） ,对 For students, the proposition composition most difficult for them is how to conceive. Because it is a black-box operation performed inside a human's brain, it can not be seen or touched, so teachers often find it mysterious and impossible to start with. The so-called proposition composition of the idea, in fact, is within the human brain, according to the expression of the needs or purpose of the external form - the symbol of the code (proposition), right