實用英語寫作技巧 (第15單元)

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麽，不是什麽。寫下定義段落時，通常把概唸或要下定義的事物置於一個大的類別中，然後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。

　　示範段落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示範段落分析

　　主題句：A pencil is an instrument for writing on paper.細節：shape，material

　　15.3關於如何寫下定義段落

　　1）以正式的定義開始

　　一個正式的定義段落通常把要定義的術語置於一個概類中，然後指出該術語與其它同類別事物有什麽不同。在示範段落15－1中，要定義的術語是“pencil”，屬於概類“instrument”。

　　2）用描述、擧例或比較對比方法擴充定義

　　在正式的定義之後，必須更詳細地解釋該術語的意思，在示範段落15－1中用的是描述法，在示範段落13－1中，擴充“courage”概唸用的是擧例法。比較對比法也可以用於擴充定義，對比法陳述該事物不是什麽，比較法陳述該事物象什麽。

　　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.