先天(tian)功(gong)(gong),武俠(xia)小(xiao)說中絕學(xue)。《射雕(diao)英雄(xiong)傳(chuan)》中是「中神(shen)通(tong)」王重陽的絕學(xue)。而其他書中解釋為(wei)呼(hu)吸吐納的練功(gong)(gong)之(zhi)法(fa),講究(jiu)抱元守(shou)(shou)一,欲(yu)練此(ci)(ci)功(gong)(gong),身如處(chu)子,不(bu)動如山,動如脫兔,呼(hu)先天(tian)下(xia)之(zhi)憂(you)而憂(you),后(hou)天(tian)下(xia)之(zhi)樂而樂。修真活計(ji)有何憑,心死群情今不(bu)生。精(jing)氣(qi)充盈(ying)功(gong)(gong)行(xing)具,靈光(guang)照(zhao)耀滿神(shen)京,秘語師傳(chuan)悟本初,來時無(wu)欠去無(wu)余。神(shen)則(ze)守(shou)(shou),身則(ze)守(shou)(shou),此(ci)(ci)功(gong)(gong)乃道家獨門不(bu)傳(chuan)之(zhi)秘,以祛百(bai)病(bing)、調虛實(shi),治療(liao)沉重內(nei)傷(shang)。此(ci)(ci)功(gong)(gong)極(ji)(ji)耗內(nei)力(li),需以高深內(nei)功(gong)(gong)為(wei)輔(fu)方可學(xue)之(zhi),當達于(yu)極(ji)(ji)限(xian)時,能相觸無(wu)聲,空中暗勁橫流,風力(li)激蕩(dang),功(gong)(gong)法(fa)里(li)的奧秘能使人潛能意識被激發(fa)到極(ji)(ji)限(xian),武學(xue)自會步入深不(bu)可測之(zhi)化(hua)境。
在金(jin)庸(yong)最初的小說創作中,「先(xian)天(tian)功(gong)(gong)」是「南(nan)(nan)帝(di)」段智(zhi)(zhi)興的絕學,而「中神(shen)通(tong)」王(wang)重陽(yang)的絕學卻是「一陽(yang)指(zhi)」。后(hou)來創作《天(tian)龍八(ba)部》將「一陽(yang)指(zhi)」改成(cheng)(cheng)「大理段氏」武學。因此(ci),在修(xiu)訂時《射雕英雄傳》、《神(shen)雕俠(xia)侶(lv)》、《倚天(tian)屠(tu)龍記(ji)》、《天(tian)龍八(ba)部》這四部小說時,為(wei)了(le)能(neng)夠前後呼應,互(hu)相對(dui)照,特意(yi)將王(wang)重陽(yang)與段智(zhi)(zhi)興的絕技(ji)交換,曾打敗(bai)「西(xi)毒」歐陽(yang)鋒(feng)(feng)(feng)的王(wang)重陽(yang)傳之(zhi)以(yi)(yi)法,將「先(xian)天(tian)功(gong)(gong)」以(yi)(yi)「一陽(yang)指(zhi)」使出,以(yi)(yi)剋(ke)制(zhi)「蛤蟆(ma)功(gong)(gong)」,以(yi)(yi)免造成(cheng)(cheng)段智(zhi)(zhi)興在第一次「華山論劍」時,身負能(neng)夠克(ke)制(zhi)「西(xi)毒」歐陽(yang)鋒(feng)(feng)(feng)的武功(gong)(gong)卻只是與「西(xi)毒」戰成(cheng)(cheng)平手的古怪結果(guo)。王(wang)重陽(yang)徒弟(di)(di)「全真七子」跟師弟(di)(di)「老頑童」周伯通(tong)均未獲得傳授,僅與「南(nan)(nan)帝(di)」段智(zhi)(zhi)興交換過「一陽(yang)指(zhi)」,用意(yi)是要(yao)「南(nan)(nan)帝(di)」擁(yong)有剋(ke)制(zhi)「西(xi)毒」歐陽(yang)鋒(feng)(feng)(feng)之(zhi)能(neng)。「先(xian)天(tian)功(gong)(gong)」配合「一陽(yang)指(zhi)」除了(le)可以(yi)(yi)完全對(dui)付歐陽(yang)鋒(feng)(feng)(feng)外,也(ye)可以(yi)(yi)祛百病、調虛(xu)實(shi),治療沉重內傷。
在(zai)不(bu)同(tong)(tong)小說描(miao)(miao)述里有(you)不(bu)同(tong)(tong)作(zuo)用(yong)(yong),上(shang)官鼎(ding)小說《沉(chen)沙(sha)谷》描(miao)(miao)述:「全(quan)(quan)真(zhen)(zhen)教」和(he)(he)「少林(lin)(lin)(lin)派(pai)」是(shi)最(zui)敝(bi)帚自珍,天(tian)(tian)下(xia)所(suo)矚目的(de)就(jiu)是(shi)「先(xian)天(tian)(tian)罡氣(qi)」。全(quan)(quan)真(zhen)(zhen)與少林(lin)(lin)(lin)雖然在(zai)取勁(jing)上(shang)有(you)柔剛之(zhi)別(bie),但(dan)天(tian)(tian)下(xia)的(de)武(wu)學(xue)是(shi)萬變不(bu)離其(qi)宗,而(er)以(yi)「人」為原則(ze)的(de)。況(kuang)且,兩派(pai)的(de)「先(xian)天(tian)(tian)氣(qi)功(gong)」又是(shi)同(tong)(tong)屬一(yi)個范圍的(de)事物。許(xu)多「全(quan)(quan)真(zhen)(zhen)派(pai)」的(de)功(gong)訣上(shang)不(bu)夠份量的(de)地(di)方(fang),拿「少林(lin)(lin)(lin)心(xin)(xin)法(fa)」一(yi)加對照,便瞭然於(wu)胸(xiong)了,而(er)相(xiang)反的(de),「少林(lin)(lin)(lin)心(xin)(xin)法(fa)」的(de)缺點(dian)也可(ke)以(yi)用(yong)(yong)全(quan)(quan)真(zhen)(zhen)之(zhi)長來(lai)補救。少林(lin)(lin)(lin)和(he)(he)全(quan)(quan)真(zhen)(zhen)佛道兩門至高(gao)武(wu)學(xue)水(shui)乳交(jiao)融,少林(lin)(lin)(lin)和(he)(he)全(quan)(quan)真(zhen)(zhen)的(de)心(xin)(xin)法(fa)一(yi)旦(dan)合并(bing),舉世無敵(di)!使用(yong)(yong)者(zhe):陸介《長干行》描(miao)(miao)述:流(liu)落(luo)於(wu)關外(wai)「天(tian)(tian)池派(pai)」。當年「全(quan)(quan)真(zhen)(zhen)教」仗(zhang)以(yi)威(wei)攝武(wu)林(lin)(lin)(lin),幾達(da)百馀年之(zhi)久,後(hou)來(lai)全(quan)(quan)真(zhen)(zhen)沒落(luo),這(zhe)種武(wu)功(gong)失傳(chuan),方(fang)有(you)少林(lin)(lin)(lin)武(wu)當等派(pai)興起(qi)(qi),算起(qi)(qi)來(lai),這(zhe)「先(xian)天(tian)(tian)功(gong)」正(zheng)(zheng)是(shi)武(wu)學(xue)之(zhi)源。當掌(zhang)力(li)(li)達(da)於(wu)極限時,能(neng)相(xiang)觸(chu)無聲(sheng),卻最(zui)易傷(shang)人內腑(fu),這(zhe)種功(gong)夫(fu),有(you)個名稱(cheng)叫做「否極泰來(lai)」,正(zheng)(zheng)是(shi)物極必(bi)反的(de)道理,掌(zhang)力(li)(li)能(neng)不(bu)聞一(yi)些聲(sheng)響,空中(zhong)暗勁(jing)橫流(liu),風力(li)(li)激蕩。使用(yong)(yong)者(zhe):「定天(tian)(tian)一(yi)戟」高(gao)戰。