先天功,武俠小說(shuo)中(zhong)絕學(xue)。《射(she)雕英雄傳(chuan)(chuan)》中(zhong)是(shi)「中(zhong)神通」王重陽的(de)絕學(xue)。而(er)其他書中(zhong)解(jie)釋為呼吸吐納(na)的(de)練功之(zhi)(zhi)法(fa),講究(jiu)抱元(yuan)守一,欲(yu)練此(ci)功,身如處子(zi),不動如山,動如脫兔,呼先天下(xia)之(zhi)(zhi)憂(you)而(er)憂(you),后天下(xia)之(zhi)(zhi)樂(le)而(er)樂(le)。修真活計有何憑,心死群(qun)情今不生。精氣(qi)充盈功行(xing)具,靈光照耀滿神京,秘語(yu)師傳(chuan)(chuan)悟本(ben)初,來時無欠去無余。神則(ze)守,身則(ze)守,此(ci)功乃道(dao)家獨門不傳(chuan)(chuan)之(zhi)(zhi)秘,以(yi)祛百病、調虛(xu)實,治療沉(chen)重內傷。此(ci)功極耗內力,需以(yi)高深內功為輔方可學(xue)之(zhi)(zhi),當達于(yu)極限時,能(neng)相觸無聲(sheng),空中(zhong)暗勁橫流,風力激(ji)蕩,功法(fa)里的(de)奧秘能(neng)使人潛(qian)能(neng)意識被激(ji)發(fa)到極限,武學(xue)自(zi)會(hui)步入(ru)深不可測之(zhi)(zhi)化(hua)境。
在(zai)(zai)金庸最初的(de)(de)(de)小說創作中,「先(xian)天(tian)(tian)功(gong)(gong)(gong)」是「南(nan)帝」段智(zhi)興的(de)(de)(de)絕學,而「中神(shen)通(tong)」王重(zhong)陽(yang)(yang)的(de)(de)(de)絕學卻是「一(yi)陽(yang)(yang)指」。后來創作《天(tian)(tian)龍八部》將(jiang)「一(yi)陽(yang)(yang)指」改(gai)成「大理段氏」武(wu)學。因此,在(zai)(zai)修訂時《射雕英雄傳(chuan)》、《神(shen)雕俠侶(lv)》、《倚天(tian)(tian)屠龍記》、《天(tian)(tian)龍八部》這四部小說時,為(wei)了能(neng)夠前後呼應,互相對(dui)照(zhao),特(te)意將(jiang)王重(zhong)陽(yang)(yang)與(yu)段智(zhi)興的(de)(de)(de)絕技交換,曾打敗(bai)「西毒(du)(du)」歐(ou)陽(yang)(yang)鋒的(de)(de)(de)王重(zhong)陽(yang)(yang)傳(chuan)之以(yi)法,將(jiang)「先(xian)天(tian)(tian)功(gong)(gong)(gong)」以(yi)「一(yi)陽(yang)(yang)指」使(shi)出,以(yi)剋(ke)制「蛤蟆功(gong)(gong)(gong)」,以(yi)免造成段智(zhi)興在(zai)(zai)第(di)一(yi)次(ci)「華山論劍」時,身負能(neng)夠克制「西毒(du)(du)」歐(ou)陽(yang)(yang)鋒的(de)(de)(de)武(wu)功(gong)(gong)(gong)卻只是與(yu)「西毒(du)(du)」戰(zhan)成平手(shou)的(de)(de)(de)古怪(guai)結果。王重(zhong)陽(yang)(yang)徒弟「全真七子」跟師弟「老頑童(tong)」周伯通(tong)均(jun)未獲得(de)傳(chuan)授,僅與(yu)「南(nan)帝」段智(zhi)興交換過「一(yi)陽(yang)(yang)指」,用意是要「南(nan)帝」擁有剋(ke)制「西毒(du)(du)」歐(ou)陽(yang)(yang)鋒之能(neng)。「先(xian)天(tian)(tian)功(gong)(gong)(gong)」配合「一(yi)陽(yang)(yang)指」除了可以(yi)完全對(dui)付歐(ou)陽(yang)(yang)鋒外,也可以(yi)祛百(bai)病、調虛實(shi),治療沉重(zhong)內傷。
在(zai)不(bu)同(tong)小說(shuo)描述(shu)(shu)里有(you)不(bu)同(tong)作用,上官鼎小說(shuo)《沉(chen)沙谷》描述(shu)(shu):「全(quan)(quan)真(zhen)教(jiao)(jiao)」和「少(shao)林(lin)派(pai)」是(shi)最(zui)(zui)敝(bi)帚(zhou)自珍(zhen),天(tian)(tian)下所矚目的(de)就(jiu)是(shi)「先天(tian)(tian)罡氣」。全(quan)(quan)真(zhen)與少(shao)林(lin)雖然在(zai)取勁上有(you)柔剛之別,但天(tian)(tian)下的(de)武學(xue)是(shi)萬(wan)變不(bu)離其宗,而(er)以「人」為原則的(de)。況且(qie),兩派(pai)的(de)「先天(tian)(tian)氣功(gong)(gong)」又是(shi)同(tong)屬一個(ge)范圍的(de)事物。許多「全(quan)(quan)真(zhen)派(pai)」的(de)功(gong)(gong)訣上不(bu)夠份量的(de)地方(fang),拿(na)「少(shao)林(lin)心法(fa)」一加對照,便瞭然於胸(xiong)了,而(er)相(xiang)(xiang)反的(de),「少(shao)林(lin)心法(fa)」的(de)缺點也可以用全(quan)(quan)真(zhen)之長來(lai)補救(jiu)。少(shao)林(lin)和全(quan)(quan)真(zhen)佛(fo)道(dao)兩門(men)至高(gao)(gao)武學(xue)水乳交融(rong),少(shao)林(lin)和全(quan)(quan)真(zhen)的(de)心法(fa)一旦合并(bing),舉世無敵!使用者(zhe):陸(lu)介《長干行》描述(shu)(shu):流(liu)落於關外(wai)「天(tian)(tian)池(chi)派(pai)」。當年(nian)(nian)「全(quan)(quan)真(zhen)教(jiao)(jiao)」仗以威攝武林(lin),幾達(da)百馀年(nian)(nian)之久,後來(lai)全(quan)(quan)真(zhen)沒落,這(zhe)種(zhong)武功(gong)(gong)失傳,方(fang)有(you)少(shao)林(lin)武當等派(pai)興起,算起來(lai),這(zhe)「先天(tian)(tian)功(gong)(gong)」正(zheng)是(shi)武學(xue)之源。當掌(zhang)力(li)達(da)於極(ji)(ji)限時,能相(xiang)(xiang)觸無聲(sheng),卻最(zui)(zui)易傷人內腑,這(zhe)種(zhong)功(gong)(gong)夫,有(you)個(ge)名稱叫(jiao)做「否極(ji)(ji)泰來(lai)」,正(zheng)是(shi)物極(ji)(ji)必(bi)反的(de)道(dao)理,掌(zhang)力(li)能不(bu)聞一些聲(sheng)響,空中暗勁橫(heng)流(liu),風力(li)激蕩。使用者(zhe):「定(ding)天(tian)(tian)一戟」高(gao)(gao)戰。