信息結構是把語言組織成信息單位（information unit）的結構。每一個信息單位是由已知信息（given information）和新信息（new information）組織而成。語篇中的已知信息提供交際所需的背景，而新信息則在已知信息的基礎上創造出信息差，信息差決定了語篇信息的交際動力。如果數個小句主位包含的全部都是新信息，那就構建不成語篇。如果全部都是舊信息，語篇便得不到發展。一般來說，主位表達已知信息，是信息的起始點。而述位則表達新信息，是信息的中心，這也是英語句子“信息焦點尾重原則”的反映。但并不總是如此，有時為了達到特殊的表達效果，也會用主位來表達新信息。在書面語篇中，由于無法用語調來表明重要信息，所以一般要依靠語序來區分主、次信息。例如：

（1）Milgram’s experiment（T1）solves an important question in sociobiology（R1）.

（2）An important question in sociobiology(T2) is solved by Milgram’s experiment(R2).

這兩個句子中，主位和述位的不同決定了已知信息和新信息的不同，從而使得第一句的信息中心是an important question in sociobiology，而第二句的信息中心是Milgram’s experiment。

3．銜接系統

三．語篇功能與雅思閱讀答題思路

1．主位推進及信息結構與段落主旨題和摘要題的答題策略

單個句子都有自己相對獨立的主位結構。但是語篇中的主述位并不是孤立出現的，前后句子的主位和主位、述位和述位、主位和述位之間始終存在某種有機的聯系和變化，這種聯系和變化就叫推進（progression）。隨著各句主位的向前推進，整個語篇逐步展開，直至形成一個能表達某一完整意義的整體（朱永生，2001）。對于語篇的主位推進模式，國內外語言學家提出了很多不同的分類。其中主要有五種模式：

（1）主位同一型（亦稱平衡型）：主位（部分）相同，述位不同

T1+R1→T2(=T1)+R2→T3(=T1)+R3

（2）述位同一型（亦稱集中型）：主位不同，述位（部分）相同

雅思閱讀涉及語篇主旨的主要題型是List of Headings（選配段落標題），考查對文章中各段中心思想的把握。答題可利用最有可能是主題句的首次尾中句分別與標題選項逐一對應，選配最佳答案。而在段落沒有主題句的情況下，則可以通過分析語篇的主位推進模式，了解其信息結構和分布動態，把握作者的思路流程或序列，并結合該題型的命題特點，重點關注主、述位信息鏈條上的邏輯關系切換、信息銜接上的重復（或強調）等環節，從而準確地解讀作者在語篇中要表達的主要意思。而對于Summary（摘要題），題干語篇的主位推進模式也會為答案的語意預判提供一定的線索。已有學者對中外學術期刊文章摘要的主位推進模式做過分析統計，結果是派生型居多。而筆者對雅思摘要題題干的分析統計表明，其主位推進模式以延續型、集中型和平衡型為主。

例1．劍橋5/Test3/Reading Passage2/Q15 Paragraph D (List of Headings)

Choose the correct heading for paragraphs B and D-F from the list of headings.

 Paragraph D（共4個句子：S1-S4）

(S1)Once north of Cairo,[復項主位T1]‖most of the Nile water is diverted into more than 10,000 kilometers of irrigation canals and only a small proportion reaches the sea directly through the rivers in the delta[述位R1].(S2)The water in the irrigation canals[單項主位T2（=R1）]‖is still or very slow-moving and thus cannot carry sediment, Stanley explains[述位R2].(S3)The sediment[單項主位T3（=R2）]‖sinks to the bottom of the canals and then is added to fields by farmers or pumped with the water into the four large freshwater lagoons that are located near the outer edges of the delta[述位R3].(S4)So very little of it[復項主位T4（=T3）]‖actually reaches the coastline to replace what is being washed away by the Mediterranean currents[述位R4].

第一句的述位（water is diverted into irrigation canals）是第二句的主位（water in the irrigation canals），第二句的述位（cannot carry sediment）是第三句的主位（The sediment），第四句的主位（very little of it）和第三句的主位相同。這種延續型和平衡型主位推進模式構建了該語篇的語意框架，表明了語篇中的信息流程和所要傳遞的信息焦點，即關于irrigation canals和sediment的相互關系。因此可以判定標題選項“Effects of irrigation on sedimentation”為正確答案。

例2．劍橋4/Test4/Reading Passage3/Q31 Section E (List of Headings)

Choose the correct heading for sections A and C-E from the list of headings. 

(S1)Just as the time when it became obvious that health-care resources could not possibly meet the demands being made upon them,[句項主位T1]‖people were demanding that their fundamental right to health-care be satisfied by the state[述位R1].(S2)The second set of more specific changes that have led to the present concern about the distribution of health-care resources[句項主位T2(=T1＊)]‖stems from the dramatic rise in health costs in most OECD countries, accompanied by large-scale demographic and social changes which have meant, to take one example, that elderly people are now major (and relatively very expensive) consumers of health-care resources[述位R2].(S3)Thus in OECD countries as a whole,[復項主位T3]‖health costs increased from 3.8% of GDP in 1960 to 7% of GDP in 1980, and it has been predicted that the proportion of health costs to GDP will continue to increase.(In theUSthe current figure is about 12% of GDP, and inAustraliaabout 7.8% of GDP.)[述位R3(=R2)]

(S4)As a consequence, during the 1980s[復項主位T4]‖a kind of doomsday scenario (analogous to similar doomsday extrapolations about energy needs and fossil fuels or about population increases) was projected by health administrators, economists and politicians[述位R4(=R2＊)].(S5)In this scenario,[單項主位T5（=R4）]‖ever-rising health costs were matched against static or declining resources[述位R5(=R3＊)].

（1）主位推進模式分析：

T1+R1→T2(=T1＊)+R2‖[派生型]→T3+R3(=R2)‖[集中型]→T4+R4(=R2＊)‖[派生型]

（2）信息銜接上的重復（或強調）：S2→S3的主位推進是集中型，述位（R

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