先(xian)天(tian)功(gong)(gong),武俠小說中(zhong)絕學。《射雕(diao)英(ying)雄傳》中(zhong)是「中(zhong)神通」王(wang)重陽的絕學。而(er)其(qi)他書中(zhong)解(jie)釋為(wei)呼吸吐(tu)納的練功(gong)(gong)之(zhi)法,講(jiang)究抱元守一,欲練此(ci)(ci)功(gong)(gong),身(shen)如(ru)處子,不動如(ru)山,動如(ru)脫兔,呼先(xian)天(tian)下之(zhi)憂而(er)憂,后天(tian)下之(zhi)樂而(er)樂。修(xiu)真(zhen)活(huo)計有何憑,心死群情今不生。精氣充(chong)盈(ying)功(gong)(gong)行具,靈光照(zhao)耀滿神京,秘(mi)語(yu)師傳悟本初,來時無(wu)欠去(qu)無(wu)余。神則守,身(shen)則守,此(ci)(ci)功(gong)(gong)乃道(dao)家獨門不傳之(zhi)秘(mi),以(yi)祛百病、調(diao)虛(xu)實(shi),治療沉重內傷。此(ci)(ci)功(gong)(gong)極(ji)耗內力(li),需以(yi)高(gao)深(shen)內功(gong)(gong)為(wei)輔方可(ke)學之(zhi),當達于極(ji)限時,能相觸無(wu)聲,空中(zhong)暗勁橫流,風力(li)激蕩,功(gong)(gong)法里的奧秘(mi)能使人潛(qian)能意識被激發到(dao)極(ji)限,武學自會步(bu)入深(shen)不可(ke)測之(zhi)化境(jing)。
在金庸(yong)最初(chu)的(de)(de)(de)小說(shuo)創作(zuo)中,「先天(tian)(tian)功(gong)(gong)(gong)」是「南帝(di)(di)」段智興的(de)(de)(de)絕學,而「中神(shen)通(tong)」王重(zhong)(zhong)陽(yang)(yang)的(de)(de)(de)絕學卻(que)是「一陽(yang)(yang)指(zhi)」。后來創作(zuo)《天(tian)(tian)龍(long)八(ba)(ba)部(bu)》將(jiang)「一陽(yang)(yang)指(zhi)」改成(cheng)「大理(li)段氏」武學。因此,在修(xiu)訂時《射雕英雄傳》、《神(shen)雕俠(xia)侶》、《倚天(tian)(tian)屠龍(long)記(ji)》、《天(tian)(tian)龍(long)八(ba)(ba)部(bu)》這四部(bu)小說(shuo)時,為了能(neng)夠前(qian)後呼應,互相對照,特意(yi)將(jiang)王重(zhong)(zhong)陽(yang)(yang)與段智興的(de)(de)(de)絕技交(jiao)換(huan),曾打敗「西(xi)(xi)毒(du)」歐(ou)(ou)陽(yang)(yang)鋒(feng)(feng)的(de)(de)(de)王重(zhong)(zhong)陽(yang)(yang)傳之以(yi)(yi)法,將(jiang)「先天(tian)(tian)功(gong)(gong)(gong)」以(yi)(yi)「一陽(yang)(yang)指(zhi)」使出,以(yi)(yi)剋制「蛤蟆功(gong)(gong)(gong)」,以(yi)(yi)免造成(cheng)段智興在第一次「華山論(lun)劍(jian)」時,身負能(neng)夠克制「西(xi)(xi)毒(du)」歐(ou)(ou)陽(yang)(yang)鋒(feng)(feng)的(de)(de)(de)武功(gong)(gong)(gong)卻(que)只是與「西(xi)(xi)毒(du)」戰(zhan)成(cheng)平(ping)手的(de)(de)(de)古怪結果。王重(zhong)(zhong)陽(yang)(yang)徒弟(di)「全真七子(zi)」跟師弟(di)「老頑(wan)童」周伯通(tong)均未(wei)獲得傳授(shou),僅與「南帝(di)(di)」段智興交(jiao)換(huan)過「一陽(yang)(yang)指(zhi)」,用(yong)意(yi)是要「南帝(di)(di)」擁有剋制「西(xi)(xi)毒(du)」歐(ou)(ou)陽(yang)(yang)鋒(feng)(feng)之能(neng)。「先天(tian)(tian)功(gong)(gong)(gong)」配(pei)合(he)「一陽(yang)(yang)指(zhi)」除了可以(yi)(yi)完(wan)全對付歐(ou)(ou)陽(yang)(yang)鋒(feng)(feng)外,也可以(yi)(yi)祛(qu)百病、調(diao)虛實,治療沉重(zhong)(zhong)內傷。
在不(bu)(bu)同(tong)小(xiao)說描(miao)述里有(you)不(bu)(bu)同(tong)作(zuo)用(yong)(yong),上官鼎(ding)小(xiao)說《沉沙谷》描(miao)述:「全(quan)真(zhen)(zhen)(zhen)教」和「少(shao)林(lin)(lin)(lin)派(pai)」是最(zui)敝帚自珍,天(tian)下所矚目的就是「先(xian)(xian)天(tian)罡(gang)氣」。全(quan)真(zhen)(zhen)(zhen)與(yu)少(shao)林(lin)(lin)(lin)雖然(ran)在取勁(jing)上有(you)柔剛之(zhi)別,但天(tian)下的武(wu)(wu)學是萬(wan)變不(bu)(bu)離其宗,而以(yi)「人」為原則的。況且,兩派(pai)的「先(xian)(xian)天(tian)氣功(gong)(gong)」又(you)是同(tong)屬一個范圍的事物。許(xu)多「全(quan)真(zhen)(zhen)(zhen)派(pai)」的功(gong)(gong)訣上不(bu)(bu)夠(gou)份量的地方(fang),拿「少(shao)林(lin)(lin)(lin)心(xin)(xin)法」一加對照,便(bian)瞭然(ran)於胸了,而相(xiang)反(fan)的,「少(shao)林(lin)(lin)(lin)心(xin)(xin)法」的缺點也可以(yi)用(yong)(yong)全(quan)真(zhen)(zhen)(zhen)之(zhi)長來(lai)(lai)補救。少(shao)林(lin)(lin)(lin)和全(quan)真(zhen)(zhen)(zhen)佛道兩門至高(gao)武(wu)(wu)學水乳交融,少(shao)林(lin)(lin)(lin)和全(quan)真(zhen)(zhen)(zhen)的心(xin)(xin)法一旦合(he)并,舉世(shi)無敵!使(shi)用(yong)(yong)者:陸(lu)介(jie)《長干行(xing)》描(miao)述:流(liu)落於關外「天(tian)池派(pai)」。當年「全(quan)真(zhen)(zhen)(zhen)教」仗以(yi)威(wei)攝武(wu)(wu)林(lin)(lin)(lin),幾(ji)達百馀年之(zhi)久,後來(lai)(lai)全(quan)真(zhen)(zhen)(zhen)沒落,這(zhe)種武(wu)(wu)功(gong)(gong)失傳,方(fang)有(you)少(shao)林(lin)(lin)(lin)武(wu)(wu)當等派(pai)興起,算起來(lai)(lai),這(zhe)「先(xian)(xian)天(tian)功(gong)(gong)」正是武(wu)(wu)學之(zhi)源。當掌(zhang)力達於極(ji)限時(shi),能相(xiang)觸無聲,卻最(zui)易傷人內(nei)腑,這(zhe)種功(gong)(gong)夫,有(you)個名稱叫做「否極(ji)泰來(lai)(lai)」,正是物極(ji)必反(fan)的道理,掌(zhang)力能不(bu)(bu)聞一些聲響,空(kong)中暗勁(jing)橫流(liu),風力激蕩。使(shi)用(yong)(yong)者:「定天(tian)一戟」高(gao)戰。