先天(tian)功(gong)(gong),武俠小說中絕學(xue)。《射雕英雄傳(chuan)》中是「中神(shen)通」王(wang)重(zhong)陽的(de)絕學(xue)。而(er)其他(ta)書中解釋為呼吸吐納的(de)練(lian)功(gong)(gong)之(zhi)(zhi)法,講究(jiu)抱元守一,欲練(lian)此功(gong)(gong),身(shen)如處子,不(bu)動(dong)(dong)如山(shan),動(dong)(dong)如脫兔,呼先天(tian)下(xia)(xia)之(zhi)(zhi)憂而(er)憂,后天(tian)下(xia)(xia)之(zhi)(zhi)樂(le)而(er)樂(le)。修真活計有何憑,心死群情今不(bu)生。精氣充盈功(gong)(gong)行具,靈(ling)光照耀滿(man)神(shen)京,秘語師(shi)傳(chuan)悟(wu)本初,來時無(wu)欠去無(wu)余。神(shen)則守,身(shen)則守,此功(gong)(gong)乃道家獨(du)門不(bu)傳(chuan)之(zhi)(zhi)秘,以祛百病、調虛實(shi),治療沉重(zhong)內(nei)(nei)傷(shang)。此功(gong)(gong)極耗內(nei)(nei)力,需以高深內(nei)(nei)功(gong)(gong)為輔(fu)方可(ke)學(xue)之(zhi)(zhi),當(dang)達于極限(xian)時,能(neng)相觸無(wu)聲,空中暗勁橫流,風力激蕩,功(gong)(gong)法里(li)的(de)奧秘能(neng)使人(ren)潛能(neng)意識被(bei)激發到極限(xian),武學(xue)自會步入深不(bu)可(ke)測之(zhi)(zhi)化(hua)境。
在金庸最初(chu)的(de)(de)(de)小(xiao)說創作中,「先(xian)天功(gong)」是(shi)「南帝」段(duan)智興(xing)的(de)(de)(de)絕(jue)學(xue)(xue),而「中神(shen)通」王重陽(yang)(yang)(yang)的(de)(de)(de)絕(jue)學(xue)(xue)卻(que)(que)是(shi)「一陽(yang)(yang)(yang)指(zhi)」。后來(lai)創作《天龍(long)八部》將「一陽(yang)(yang)(yang)指(zhi)」改成「大(da)理段(duan)氏」武學(xue)(xue)。因此,在修訂時《射雕(diao)英雄傳(chuan)》、《神(shen)雕(diao)俠侶(lv)》、《倚天屠龍(long)記》、《天龍(long)八部》這(zhe)四部小(xiao)說時,為了能(neng)夠前後呼應,互相對照,特意(yi)將王重陽(yang)(yang)(yang)與(yu)段(duan)智興(xing)的(de)(de)(de)絕(jue)技交(jiao)換,曾打敗「西(xi)毒(du)」歐陽(yang)(yang)(yang)鋒(feng)的(de)(de)(de)王重陽(yang)(yang)(yang)傳(chuan)之(zhi)以(yi)法,將「先(xian)天功(gong)」以(yi)「一陽(yang)(yang)(yang)指(zhi)」使出,以(yi)剋制(zhi)「蛤蟆功(gong)」,以(yi)免造成段(duan)智興(xing)在第(di)一次「華山論劍」時,身負(fu)能(neng)夠克(ke)制(zhi)「西(xi)毒(du)」歐陽(yang)(yang)(yang)鋒(feng)的(de)(de)(de)武功(gong)卻(que)(que)只是(shi)與(yu)「西(xi)毒(du)」戰(zhan)成平手(shou)的(de)(de)(de)古怪結果。王重陽(yang)(yang)(yang)徒(tu)弟(di)「全(quan)真七子(zi)」跟師弟(di)「老(lao)頑(wan)童(tong)」周伯通均未(wei)獲得傳(chuan)授,僅(jin)與(yu)「南帝」段(duan)智興(xing)交(jiao)換過「一陽(yang)(yang)(yang)指(zhi)」,用意(yi)是(shi)要「南帝」擁有剋制(zhi)「西(xi)毒(du)」歐陽(yang)(yang)(yang)鋒(feng)之(zhi)能(neng)。「先(xian)天功(gong)」配合「一陽(yang)(yang)(yang)指(zhi)」除了可以(yi)完(wan)全(quan)對付歐陽(yang)(yang)(yang)鋒(feng)外(wai),也可以(yi)祛百病、調虛(xu)實,治療(liao)沉重內傷。
在不(bu)(bu)(bu)同小說描(miao)述(shu)(shu)里有(you)不(bu)(bu)(bu)同作(zuo)用(yong)(yong),上官鼎小說《沉沙谷(gu)》描(miao)述(shu)(shu):「全(quan)真(zhen)(zhen)(zhen)教」和(he)「少林(lin)(lin)(lin)(lin)派(pai)」是(shi)最敝帚自珍(zhen),天(tian)(tian)下所(suo)矚目的(de)(de)就(jiu)是(shi)「先天(tian)(tian)罡(gang)氣(qi)」。全(quan)真(zhen)(zhen)(zhen)與少林(lin)(lin)(lin)(lin)雖然在取勁上有(you)柔剛(gang)之(zhi)別(bie),但(dan)天(tian)(tian)下的(de)(de)武(wu)學(xue)是(shi)萬變不(bu)(bu)(bu)離其宗,而(er)以(yi)「人」為原(yuan)則(ze)的(de)(de)。況且,兩派(pai)的(de)(de)「先天(tian)(tian)氣(qi)功(gong)」又是(shi)同屬一(yi)(yi)個范圍(wei)的(de)(de)事物(wu)。許多「全(quan)真(zhen)(zhen)(zhen)派(pai)」的(de)(de)功(gong)訣上不(bu)(bu)(bu)夠份量(liang)的(de)(de)地方(fang),拿「少林(lin)(lin)(lin)(lin)心法(fa)」一(yi)(yi)加對照,便瞭(liao)然於(wu)(wu)胸(xiong)了,而(er)相反的(de)(de),「少林(lin)(lin)(lin)(lin)心法(fa)」的(de)(de)缺點也可以(yi)用(yong)(yong)全(quan)真(zhen)(zhen)(zhen)之(zhi)長來補救。少林(lin)(lin)(lin)(lin)和(he)全(quan)真(zhen)(zhen)(zhen)佛道(dao)兩門至高(gao)武(wu)學(xue)水乳(ru)交融,少林(lin)(lin)(lin)(lin)和(he)全(quan)真(zhen)(zhen)(zhen)的(de)(de)心法(fa)一(yi)(yi)旦合并(bing),舉世無敵!使用(yong)(yong)者(zhe):陸(lu)介《長干行》描(miao)述(shu)(shu):流落於(wu)(wu)關外「天(tian)(tian)池派(pai)」。當年「全(quan)真(zhen)(zhen)(zhen)教」仗(zhang)以(yi)威攝武(wu)林(lin)(lin)(lin)(lin),幾達(da)百(bai)馀年之(zhi)久,後(hou)來全(quan)真(zhen)(zhen)(zhen)沒(mei)落,這種武(wu)功(gong)失傳,方(fang)有(you)少林(lin)(lin)(lin)(lin)武(wu)當等派(pai)興起,算起來,這「先天(tian)(tian)功(gong)」正是(shi)武(wu)學(xue)之(zhi)源(yuan)。當掌力(li)達(da)於(wu)(wu)極限時(shi),能相觸無聲(sheng),卻最易傷人內腑,這種功(gong)夫,有(you)個名稱叫做「否極泰來」,正是(shi)物(wu)極必反的(de)(de)道(dao)理,掌力(li)能不(bu)(bu)(bu)聞一(yi)(yi)些(xie)聲(sheng)響,空(kong)中暗勁橫(heng)流,風力(li)激(ji)蕩。使用(yong)(yong)者(zhe):「定天(tian)(tian)一(yi)(yi)戟」高(gao)戰(zhan)。