一个段落内的各个句子必须从属于一个中心，任何游离于中心思想之外的句子都是不可取的。请看下例：
JoeandIdecidedtotakethelongtripwe'dalwayswantedacrossthecountry.Wewerelikeyoungkidsbuyingourcamperandstockingitwithallthenecessitiesoflife.Bellabakesthebestrhubarbpie.WestartedoutinearlyspringfromMinneapolisandheadedwestacrossthenorthernpartofthecountry.Webothenjoyedthosepeoplewemetatthetrailerpark.Joereceivedawatchathisretirementdinner.Tooursurprise,wefoundthatwelikedthewarmsouthernregionsverymuch,andsowedecidedtostayhereinNewMexico.
MynameisRoseanna,andIliketokeepphysicallyfit.Iusedtoweightwohundredpounds,butIjoinedtheYMCAforanexerciseclassanddietprogram.InoneyearIlosteightypounds.Ifeelmuchbetterandneverwanttohavethatmuchweightonmyfive-feetframeagain.Iboughttwonewsuitcaseslastweek.EverydayIpracticejoggingthreemiles,swimmingfifteenlaps,liftingtwenty-poundweightsandplayingtennisforonehour.Mymotherwasaprematurebaby.
本段的controllingidea是liketodeepphysicallyfit，但段中有两个irrelevantsentences，一个是Iboughttwonewsuitcaseslastweek，另一个是Mymotherwasaprematurebaby。
从上面两个例子可以看出，nativespeakers同样会造出来irrelevantsentences。卷面上如果这种句子多了，造成偏题或离题，那问题就更严重了。
2、完整性
正象我们前面说得那样，一个段落的主题思想靠推展句来实现，如果只有主题句而没有推展句来进一步交待和充实，就不能构成一个完整的段落。同样，虽然有推展句，但主题思想没有得到相对圆满的交待，给读者一种意犹未尽的感觉。这样的段落也不能完成其交际功能。例如：
Physicalworkcanbeausefulformoftherapyforamindinturmoil.Workconcentratesyourthoughtsonaconcretetask.Besides,itismoreusefultowork----youproducesomethingratherthanmoreanxietyordepression.
本段的主题句是段首句。本段的两个推展句均不能回答主题句中提出的问题。什么是“amindinturmoil”（心境不平静）Physicalwork又如何能改变这种情况？为什么它能起therapy的作用？读者得不到明确的答案。由于四级统考的作文部分只要求写一篇100～120个词的三段式短文，每一段只有大约40个词左右，因此，要达到完整就必须尽可能地简明。例如：
Itisnotalwaystruethatagoodpictureisworthathousandwords.Oftenwritingismuchclearerthanapicture.Itissometimesdifficulttofigureoutwhatapicturemeans,butacarefulwritercanalmostalwaysexplainit.
段首句所表达的主题思想是一种看法，必须有具体事例加以验证。上述两个推展句只是在文字上对主题作些解释，整个段落内容空洞，简而不明。如果用一两个具体的例子的话，就可以把主题解释清楚了。比如下段：
Itisnotalwaystruethatapictureisworthathousandwords.Sometimes,picturesareprettyuselessthings.Ifyoucan'tswimandfallintheriverandstartgulpingwater,willyoubebetterofftoholdupapictureofyourselfdrowning,orstartscreaming"Help"
3、连贯性（coherence）
连贯性包括意连和形连两个方面，前者指的是内在的逻辑性，后者指的是使用转换词语。当然这两者常常是不可分割的。只有形连而没有意连，句子之间就没有内在的有机的联系；反之，只有意连而没有形连，有时行文就不够流畅。
1）、意连
Wehadanumberofclosecallsthatday.Whenwerose,itwasobviouslylateandwehadtohurrysoasnottomissbreakfast;weknewthediningroomstaffwasstrictaboutclosingatnineo'clock.Then,whenwehadbeendrivinginthedesertfornearlytwohours-----itmusthavebeenclosetonoon----theheatnearlyhidusin;theradiatorboiledoverandwehadtousemostofourdrinkingwatertocoolitdown.Bythetimewereachedthemountain,itwasouro'clockandwewereexhausted.Here,judgementranoutofusandwestartedthetoughclimbtothesummit,notrealizingthatdarknesscamesuddenlyinthedesert.Sureenough,bysixwewerestrugglingandAndrewverynearlywentdownasteepcliff,draggingMohammedandmealongwithhim.Bynine,whenthewindhowledacrosstheflatledgeofthesummit,weknewasweshiveredtogetherforwarmththatithadnotbeenourluckyday.
本段从“rose”（起床）写起，然后是吃早餐（“nottomissbreakfast”,“closingatnineo'clock”），然后是“closetonoon”，一直写到这一天结束（“Bynine--”）。
B.按位置远近排列（spatialarrangement）。例如：
Fromadistance,itlookedlikeaskinnytube,butaswegotcloser,wecouldseeitfleshoutbeforeoureyes.Itwastubular,allright,butfatterthanwecouldseefromfaraway.Furthermore,wewerealsoastonishedtonoticethatthebuildingwasreallyintwoparts:apagodasittingontopofatubularone-storystructure.Standingtenfeetaway,wecouldmarvelathowmuchofthepagodawasmadeupofglasswindows.AlmosteverythingunderthewonderfulChineseroofwasmadeofglass,unlikethetubethatitwassittingon,whichonlyhadfour.Inside,thetubewasgloomy,becauseofthelackoflight.Thenasteep,narrowstaircasetookusupinsidethepagodaandthelightchangeddramatically.Allthosewindowsletinafloodofsunshineandwecouldseeoutformilesacrosstheflatland.
本段的写法是由远及近，从远处（“fromadistance”）写起，然后“getcloser”，再到（“tenfeetaway”），最后是“insidethepagoda”……当然，按位置远近来写不等于都是由远及近。根据需要，也可以由近及远，由表及里等等。
C.按逻辑关系排列（logicalarrangement）
a.按重要性顺序排列（arrangementinorderofimportance）
Ifyouworkasasodajerker,youwill,ofcourse,notneedmuchskillinexpressingyourselftobeeffective.Ifyouworkonamachine,yourabilitytoexpressyourselfwillbeoflittleimportance.Butassoonasyoumoveonestepupfromthebottom,youreffectivenessdependsonyourabilitytoreachothersthroughthespokenorthewrittenword.Andthefurtherawayyourjobisfrommanualwork,thelargertheorganizationofwhichyouareanemployee,themoreimportantitwillbethatyouknowhowtoconveyyourthoughtsinwritingorspeaking.Intheverylargebusinessorganization,whetheritisthegovernment,thelargecorporation,ortheArmy,thisabilitytoexpressoneselfisperhapsthemostimportantofalltheskillsamancanpossess.
这一段谈的是表达能力，它的重要性与职业，身份有关，从“notneedmuchskill”或“oflittleimportance”到“moreimportant”，最后是“mostimportant”。
b.由一般到特殊排列（general-to-specificarrangement）
Ifareaderislost,itisgenerallybecausethewriterhasnotbeencarefulenoughtokeephimonthepath.Thiscarelessnesscantakeanynumberofforms.Perhapsasentenceissoexcessivelyclutteredthatthereader,hackinghiswaythroughtheverbiage,simplydoesn'tknowwhatitmeans.Perhapsasentencehasbeensoshoddilyconstructedthatthereadercouldreaditinanyofseveralways.Perhapsthewriterhasswitchedtenses,orhasswitchedpronounsinmid-sentence,sothereaderlosestrackofwhentheactiontookplaceorwhoistalking.PerhapssentenceBisnotlogicalsequeltosentenceA----thewriter,inwhoseheadtheconnectionisclear,hasnotbotheredtoprovidethemissinglink.Perhapsthewriterhasusedanimportantwordincorrectlybynottakingthetroubletolookitup.Hemaythinkthat"sanguine"and"sanguinary"meanthesamething,butthedifferenceisabloodybigone.Thereadercanonlyinferwhatthewriteristryingtoimply.
这一段谈的是awriter'scarelessness，先给出一个generalstatement作为主题句，然后通过5个＂perhaps＂加以例证。
c.由特殊到一般排列（specific-to-generalarrangement）
IdonotunderstandwhypeopleconfusemySiamesecat,Prissy,withtheoneIhadseveralyearsago,Henry.Thetwocatsareonlyalikeinbreed.Prissy,aquiet,femininefeline,lovesmedearlybutnotpossessively.Shelikestokeepherdistancefrompeople,exertherindependenceandisneversorudeastobeg,lick,orsniffunceremoniously.Herusualpostureissittingupright,eyesclosed,perfectlystill.Prissyisaverypropercat.Henry,ontheotherhand,lovedmedearlybutpossessively.Hewasmyshadowfrommorningtillnight.Heexpectedmetoconstantlyentertainhim.Henrynevercaredwhosawhimdoanything,whetheritwasdecorousornot,andheusuallyoffendedmyfriendsinsomeway.Thecatmadehimselfquitecomfortable,onthetopofthetelevision,acrossstranger'sfeetorlaps,inbeds,drawers,sacks,closets,ornooks.Thedifferencebetweenthemisimperceptibletostrangers.
本段的主题句是段首句，它仅提出一个问题：为什么两只猫会被搞混。然后对两者进行比较，末句才下结论。
2）、形连
行文的逻辑性常常要靠适当的转换词语及其他手段来实现。请读下面这一段文字并找出文中用以承上启下的词语：
Walter'sgoalinlifewastobecomeasuccessfulsurgeon.First,though,hehadtogetthroughhighschool,soheconcentratedallhiseffortsonhisstudies---inparticular,biology,chemistry,andmath.Becauseheworkedconstantlyonthesesubjects,Walterbecameproficientinthem;however,Walterforgotthatheneededtomasterothersubjectsbesidesthosehehadchosen.Asaresult,duringhisjunioryearofhighschool,WalterfailedbothEnglishandLatin.Consequently,hehadtorepeatthesesubjectsandhewasalmostunabletograduateonschedule.Finally,onJune6,Walterachievedthefirststeptowardrealizinghisgoal.
本文中起承上启下的词语有两种，一种是转换词语（transitionalwordsorphrases），另一种是起转换作用的其他连接手段（linkingdevices）。前者依次有：first,though,so,inparticular,and,because,however,besides,asaresult,both…and,consequently,and,finally.后者依次是：he,he,his,his,he,these,them,he,those,his,he,these,his.本段中共有词汇105个，所使用的转换词语及其他连接用语共26个词，约占该段总词汇量的四分之一。由此可见，掌握好transitions不仅对行文的流（smoothness）有益，而且对于学生在半个小时内写足四级短文所要求的120个词也是不无好处的。
一个段落里如果没有transitions也就很难有coherence了.我们看下面一个例子：Speakingandwritingaredifferentinmanyways.Speechdependsonsounds.Writinguseswrittensymbols.Speechdevelopedabout500000yearsago.Writtenlanguageisarecentdevelopment.Itwasinventedonlyaboutsixthousandyearsago.Speechisusuallyinformal.Thewordchoiceofwritingisoftenrelativelyformal.Pronunciationandaccentoftentellwherethespeakerisfrom.Pronunciationandaccentareignoredinwriting.Astandarddictionandspellingsystemprevailsinthewrittenlanguageofmostcountries.Speechreliesongesture,loudness,andriseandfallofthevoice.Writinglacksgesture,loudnessandtheriseandfallofthevoice.Carefulspeakersandwritersareawareofthedifferences.
本段中除了第6句开头出现一个起过渡作用的＂it＂之外，没有使用其他的过渡词语.这样，文中出现许多重复的词语，全段读起来也显得生硬而不自然。如果加上必要的过渡词语来修饰的话，这一段就成了下面一个流畅连贯的段落：
Speakingandwritingaredifferentinmanyways.Speechdependsonsounds;writing,ontheotherhand,useswrittensymbols.Speechwasdevelopedabout500000yearsago,butwrittenlanguageisarecentdevelopment,inventedonlyaboutsixthousandyearsago.Speechisusuallyinformal,whilethewordchoiceofwriting,bycontrast,isoftenrelativelyformal.Althoughpronunciationandaccentoftentellwherethespeakerisfrom,theyareignoredinwiringbecauseastandarddictionandspellingsystemprevailsinmostcountries.Speechreliesongesture,loudness,andtheriseandfallofthevoice,butwritinglacksthesefeatures.Carefulspeakersandwritersareawareofthedifferences．
4、有损连贯性的几种情况：
考生在写作中经常出现下面几种错误：
1、不必要的改变时态，比如：
Inthemovie,RobertRedfordwasaspy.Hegoestohisofficewherehefoundeverybodydead.Otherspieswantedtokillhim,sohetakesrefugewithJulieChristie.Atherhouse,hehadwaitedfortheheattodiedown,buttheycomeafterhimanyway.
2、不必要的改变单复数，比如：
Everybodylooksforsatisfactioninhislife.Theywanttobehappy.Butifheseeksonlypleasureintheshortrun,thepersonwillsoonrunoutofpleasureandlifewillcatchuptohim.Theyneedtopursuethedeeperpleasureofsatisfactioninworkandinrelationships.
３、不必要的改变人称，比如：
Nowmorethanever,parentsneedtobeintouchwiththeirchildren'sactivitiesbecausemodernlifehasthetendencytocausecleavagesinthefamily.Youneedtoarrangefamilylikeitsothatfamilymemberswilldothingstogetherandknowoneanother.Youneedtogiveupisolatedpleasuresofyourownandrealizethatparentshaveasetofobligationstosponsortogethernessandthereforesponsorknowledge.
因此写作中，一定要注意时态，人称以及数的变化是否正确，要注意保持一致。