第十五單元 推展段落方法之七——下定義法

15．1下定義法

下定義（definition）就是解釋某事物是什么，不是什么。寫下定義段落時(shí)，通常把概念或要下定義的事物置于一個(gè)大的類別中，然后解釋該事物與同一類別的其它事物有何不同。下定義法多用作推展段落的輔助方法。

示范段落15－1

A pencil is an instrument for writing on paper．It is of cylindrical shape and can be held between the first two fingers of the hand．It is about 6 inches long and 1／4 inch wide．At the end there is usually an eraser attached to the pencil by a surrounding metal band．Lead is the material which is used in making the marks on the paper，and a sharpener is needed to keep the pencil in good working order．Pencils are made of various kinds of wood．

15．2示范段落分析

主題句：A pencil is an instrument for writing on paper．細(xì)節(jié)：shape，material

15．3關(guān)于如何寫下定義段落

1）以正式的定義開始

一個(gè)正式的定義段落通常把要定義的術(shù)語置于一個(gè)概類中，然后指出該術(shù)語與其它同類別事物有什么不同。在示范段落15－1中，要定義的術(shù)語是“pencil”，屬于概類“instrument”。

2）用描述、舉例或比較對(duì)比方法擴(kuò)充定義

在正式的定義之后，必須更詳細(xì)地解釋該術(shù)語的意思，在示范段落15－1中用的是描述法，在示范段落13－1中，擴(kuò)充“courage”概念用的是舉例法。比較對(duì)比法也可以用于擴(kuò)充定義，對(duì)比法陳述該事物不是什么，比較法陳述該事物象什么。

Exercise 15-1

Directions：Read the following paragraph，point out the topic sentence and find out what method（s）are used to expand the defintion．

Chemistry is that branch of science which has the task of investigating the materials out of which the universe is made．It is not concerned with the forms into which they may be fashioned．Such objects as chairs，tables，vases，bottles，or wires are of no significance in chemistry；but such substances as glass，wool，iron，sulfur，and clay，as the materials out of which they are made，are what it studies．Chemistry is concerned not only with the composition of such substances，but also with their inner structure．

Topic Sentence：____________________________________________

Method（s） used：_______________________________________

Exercise 15－2

Directions：The definition of“an ice－box”can be，“An ice－box is an appliance for storing food at low temperature．”Now use the method of description to expand the definition．

An ice－box is an appliance for storing food at low temperature．

_________________________________________

Exercise 15-3

Directions：Give the defintion of friendship and then use an example to expand your definition．

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