说明文是以说明为主要表达方式用来说明事物，阐明事理的一种文体。它通过揭示概念来说明事物的特征、本质及其规律性，给人准确的科学知识或正确思想。一般可分为实体事物说明和抽象事物说明两大类，词典、教材、论文、实验报告、产品说明书、广告、解说词及科学小品等都属于说明文。
        
        按写作方法,英语说明文主要分为下面六种类型:
        
        1.例证法
        
         这是用具体例子来说明人或事物的特征、本质及其规律的方法,所用例子必须有代表性、典型性,能体现人或事物的本质特征。这是用特殊来说明一般的方法。通常在主题句后,用 For example 或 For instance 等短语引导出具体的例子。例如:
        
        Our life today depends very much on energy. For example, machines have made our life easier than it used to be. The machines use energy, and energy is needed for heating, lighting, communications, carrying goods-everything. Factories use a great deal of energy to make the things that we use and buy and sell.
        
        这段主要是讲能源问题。第一句为主题句,概括地说出"我们目前的生活很大程度上依赖能源"。接着用举例的方法从三方面说明能源的作用。
        
        2.定义法
        
        下定义就是给说明对象一个明确概念。这是科学而严密的说明方法。它既能揭示事物的本质特征,勾勒其大概,描绘其轮廓,同时也能确定事物的范围和界限。下定义是多方面的,可以给人、事物、思想等下定义。例如:
        
        An ideal teacher must have the following characteristics. He should know his subject, but he can make mistakes if he is willing to learn. His personality is as important as his scholarship. An ideal teacher must be enthusiastic. He should be a bit of an actor and he shouldn't be afraid to show his feelings and express his likes and dislikes. An ideal teacher is one who grows, learns, and improves himself along with his students.
        
        本段的展开是通过对"一个模范教师"下定义的方法,关键词"ideal teacher"在文中多次重复,能加深读者的印象。