信Trust
善心所之首。心淨為性，樂善為業。
漢zh · Xuanzang 譯
善心所之首。心淨為性，樂善為業。
經
[共傳] 《雜阿含經》卷二十六（五根相應），佛告比丘：
何等為信根？若比丘於如來所起信心，根本堅固，諸天、魔、梵、沙門、婆羅門，無能及者，是名信根。
[大乘] 《華嚴經·賢首品》：
信為道元功德母，長養一切諸善根。 斷除疑網出愛流，開示涅槃無上道。
論
《成唯識論》卷六：
云何為信？於實、德、能深忍樂欲、心淨為性。對治不信、樂善為業。
按：三層引文呈信義之深化——阿含立信為一根（indriya）「諸天魔梵無能及」；大乘升信為「道元功德母」一切善法之所從生；唯識論拆信為三層結構（實/德/能 × 深忍/心淨/樂欲），詳如下梵段。三層皆共許信為善心必伴之首，非大乘特有。
梵saṃskṛta
śrad-（古義 satya「真實」per Naighaṇṭuka；印歐祖語層面 *ḱr̥d- 反映「心」，與拉丁 cor、希臘 kardía、英文 heart 同源）+ √dhā（置）——印歐祖語 *ḱred-dʰh₁-「以心置於彼」。同源：拉丁 crēdō、古阿維斯陀 zrazdā-、古愛爾蘭 creitid、吐火羅 käryā。
《阿毘達磨集論》（阿毘達磨-samuccaya，Pradhan 校本，梵文殘卷段）：
śraddhā katamā / astitva-guṇavattva-śaktatveṣv abhisaṃpratyayaḥ prasādo 'bhilāṣaḥ / chanda-sanniśrayadāna-karmikā //
何為信？於實（astitva）、德（guṇavattva）、能（śaktatva）三事，起深確信（abhisaṃpratyaya）、澄淨（prasāda）、樂欲（abhilāṣa）為性。為欲（chanda）作所依為業。
| 對境（object） | 心狀（response） | 玄奘譯 |
|---|---|---|
| astitva 實 | abhisaṃpratyaya 深忍 | 於實…深忍 |
| guṇavattva 德 | prasāda 心淨 | 於德…心淨 |
| śaktatva 能 | abhilāṣa 樂欲 | 於能…樂欲 |
按：3×3 結構即《成唯識論》「於實、德、能深忍樂欲、心淨為性」之梵文原型——玄奘逐節對譯，三對境配三心狀無一脫漏。功能子句 chanda-sanniśrayadāna-karmikā「為欲（→#14）作所依」明置信於修習鏈之上游：信→欲→精進→念→定→慧。其反面為 #48 āśraddhya（不信），三項皆加 a- 前綴（anabhisaṃpratyaya / aprasāda / anabhilāṣa）為此 3×3 之 perfect 正反對。
巴pāḷi
遍美心所（sobhana-sādhāraṇa 心所（cetasika）），隨一切善心而起。
經
《相應部·根相應》SN 48.10 Dutiyavibhaṅgasutta（同見 SN 48.9 Paṭhamavibhaṅgasutta、《增支部》AN 5.14 Vitthatasutta 之信力定義；三經逐字同句）：
Katamañca, bhikkhave, saddhindriyaṃ? Idha, bhikkhave, ariyasāvako saddho hoti, saddahati tathāgatassa bodhiṃ — "iti pi so bhagavā ... buddho bhagavā" ti — idaṃ vuccati, bhikkhave, saddhindriyaṃ.
何為信根？比丘！於此聖弟子有信，信如來之菩提——「彼世尊為阿羅漢、正等覺者……佛、世尊」——是名信根。
《經集》Sn 182（CSCD 編 Sn 184；同偈亦見《相應部》SN 10.12 同名 Āḷavaka 經）：
Saddhīdha vittaṃ purisassa seṭṭhaṃ, dhammo suciṇṇo sukhamāvahāti; saccaṃ have sādutaraṃ rasānaṃ, paññājīviṃ jīvitamāhu seṭṭhaṃ.
信為此世人之最上財， 善行之法引樂； 真實實為味中最甜， 活以智慧者，所稱最勝。
論
《清淨道論》XIV.140（行蘊·美心所）以四相分析信：
| 四相 | Pāli | 義 |
|---|---|---|
| 相 lakkhaṇa | saddahana / okappana | 信任、確信 |
| 業 rasa（一） | pasādana（如水清珠 udakappasādaka-maṇi） | 令澄淨 |
| 業 rasa（二） | pakkhandana（如渡瀑流者 oghuttaraṇo viya；cf. Sn 184） | 躍入 |
| 現 paccupaṭṭhāna | akālussiya / adhimutti | 無濁、決意 |
| 足處 padaṭṭhāna | saddheyya-vatthu / sotāpattiyaṅgāni | 值信之事、四預流支 |
按：Vism 兩 functions（pasādana + pakkhandana）——澄淨與躍入並陳，即「信」之兩面：靜（沉澱煩惱）與動（投身渡岸）。pakkhandana 喻互參 Sn 184「saddhā tarati oghaṃ」（信能渡瀑流），與 Sn 182 同 Āḷavaka 場景，南傳經內部 互文。單舉水清珠喻則為片面。
漢綜述zh-synthesis
「信」之梵文 śrad-dhā 為動詞性合成——śrad-（古義 satya「真實」，依《尼祿多》 Naighaṇṭuka iii.10；於印歐祖語層面 *ḱr̥d- 反映「心」，與拉丁 cor、希臘 kardía、英文 heart 同源）+ √dhā（置）——構擬印歐祖語形 *ḱred-dʰh₁-，意為「以心置於彼」。同源詞遍佈印歐語系：拉丁 crēdō、古阿維斯陀 zrazdā-、古愛爾蘭 creitid、吐火羅 käryā。英文 faith（< 拉丁 fidēs < 印歐 *bʰeydʰ-「誓、結」）為不同 PIE 根之 false friend——以 faith 譯 śraddhā 將之置於錯誤之印歐語族。「信」之動詞性核心為「置心」——非靜態之命題式之相信（belief-that），而是動態之「以心置於」。⭐ 跨 cluster 詞源呼應：Asg 信定義之三 svabhāva 之一 prasāda（心淨）與色法 5 根之 rūpa-prasāda（淨色根，→#60）共印歐祖語 √*sed-「沉澱方澄清」動性——心之澄明與根之澄明共此動性結構；瑜伽行派論藏未明畫此連結，然詞彙呼應穩固（詳 →#60 §梵段 + §漢綜述 之 prasāda 跨 dharma 觀察）。
《阿毘達磨集論》（Abhidharma-samuccaya）之定義揭示一 3×3 結構：三對境（實 astitva / 德 guṇavattva / 能 śaktatva）配三心狀（深忍 abhisaṃpratyaya / 心淨 prasāda / 樂欲 abhilāṣa）。玄奘《成唯識論》逐字對譯為「於實、德、能深忍、樂欲、心淨為性」——三對境配三心狀無一脫漏。功能子句 chanda-sanniśrayadāna-karmikā「為欲（→#14）作所依」明置信於修習鏈之上游：信→欲→精進→念→定→慧。其反面 →#48 不信 āśraddhya 為加 a- 前綴之對偶（anabhisaṃpratyaya / aprasāda / anabhilāṣa），為 51 心所中之 3×3 對偶結構之代表例（其他鏡像架構詳序 §4.5；→#50 放逸 ↔ #29 不害 為 4 軸完整反相對偶）。
三系統皆以信為善心必伴之首，無有例外：阿含立信為五根之一（saddhindriya），「諸天魔梵無能及」；瑜伽行派列為善十一之首；南傳論藏列為遍美心所（sobhana-sādhāraṇa cetasika），隨一切善心而起。Pāli 經典證據密度尤深——《相應部》SN 48.9《第一分別經》、SN 48.10《第二分別經》、《增支部》AN 5.14《廣說經》三經之 saddhindriya 定義逐字同句；《經集》Sn 182 與 SN 10.12《Āḷavaka 經》同偈兩傳並陳。三重尼柯耶平行加兩傳並陳，置此教義於共傳證據密度之最深層——非大乘特立。
《清淨道論》XIV.140 立信之兩重業用——pasādana（澄淨，如水清珠 udakappasādaka-maṇi）與 pakkhandana（躍入，如渡瀑流者 oghuttaraṇo viya）——並陳兩面而不可拆。澄淨乃靜（沉澱煩惱），躍入乃動（投身渡岸）；單舉一面則失。pakkhandana 之喻互參於《經集》Sn 184「saddhā tarati oghaṃ」（信能渡瀑流），與 Sn 182 同 Āḷavaka 場景，為南傳經內部之互文。瑜伽修習鏈以信為先決條件——欲（→#14）之能起，必賴所信之預立為「實、德、能」三事之可趨向；無信，則修習鏈之首環缺。
本譯選「信」為玄奘之既譯，亦因「信」於漢文已含動詞性——「信任」「信奉」皆動作義；「信仰」於現代漢語義過於宗教化而失 śraddhā 之認識論維度。英譯選 trust 而非 faith，正因 trust 在英語亦保留動詞性（"to trust"）；faith 已由基督教傳統定型為命題性之 belief-that，且 PIE 根異（< *bʰeydʰ-「誓、結」），為 false friend。雙譯之選擇皆回歸「以心置於彼」之動詞核心——這是梵文形態學所給出之深層架構，亦為信 śrad-dhā ↔ 定（→#17）sam-ā-dhā 共 √dhā 根之 doctrinal 證據：別境五修習鏈之首尾兩環皆「置心」之動詞派生。
信 ——於實、德、能深忍、樂欲、心淨為性。對治不信、樂善為業。
英綜述en-synthesis
Sanskrit śrad-dhā and Pāli sad-dhā compound śrad- + √dhā ("to place"), reflecting PIE *ḱred-dʰh₁- — literally "to place the heart." The cognate set is precise: Latin crēdō (whence English credo, credit, credence, creed), Old Avestan zrazdā-, Old Irish creitid, Tocharian käryā. Two layers must be distinguished: synchronically in Sanskrit śrat means satya ("truth," per Naighaṇṭuka iii.10), not "heart"; the cardiac sense surfaces only at the PIE level via *ḱr̥d-, which gives Latin cor, Greek kardía, and English heart. The deep root that makes śraddhā "heart-placing" is the same root that gives English the word heart itself. English faith, by contrast, descends from a different root entirely — Latin fidēs < PIE *bʰeydʰ- ("oath, bond"). Rendering śraddhā as "faith" therefore mis-places it across IE word-families. Trust — Germanic, ultimately PIE *deru- ("firm, steadfast") — is no closer etymologically, but it carries the right semantic load: confidence directed toward what one has good reason to rely on, not unconditional belief.
The Sanskrit definition recovered from Asaṅga's Abhidharma-samuccaya exposes a 3×3 architecture that Xuanzang's translation preserves intact: three objects — astitva (existence/reality), guṇavattva (virtue/qualities), śaktatva (capability/power) — paired with three corresponding mental states — abhisaṃpratyaya (firm conviction), prasāda (serene clarity), abhilāṣa (longing). Faith is not a single attitude but a triple disposition keyed to a triple object: confidence in what is, clarity toward what is good, aspiration for what can be done. Its function (karman) is to provide the foundation for chanda (zeal/will). The cultivation order śraddhā → chanda → adhimokṣa → smṛti → samādhi → prajñā — faith → will → resolve → mindfulness → concentration → wisdom — places faith structurally upstream of will: aspiration cannot arise without something already trusted as both possible and worth pursuing.
Śraddhā heads the eleven wholesome mental factors (善十一) in Yogācāra, sits among the kuśala-mahābhūmika in Sarvāstivāda, and parallels the sobhana-sādhāraṇa (universal-beautiful) factors in the Theravāda Abhidhamma. All three systems agree on its structural place: faith is co-present with every wholesome moment of mind. The Pāli canonical attestation is unusually deep — saddhindriya appears with byte-identical formula across SN 48.9, SN 48.10, and AN 5.14, attesting saddhā simultaneously as indriya (faculty) and bala (power); the Āḷavaka teaching at Sn 1.10 is preserved redundantly at SN 10.12. Triple Nikāya attestation in the indriya/bala lists, plus double redaction of the Āḷavaka exchange, plus verbatim agreement between Asaṅga's Sanskrit and Xuanzang's Chinese, places this doctrine at the strongest level of canonical attestation the corpus offers — a 共傳 (shared-canon) doctrine, not a sectarian elaboration.
Visuddhimagga XIV.140 names two functions for saddhā: pasādana — clarifying, like a water-clearing gem (udakappasādaka-maṇi) that settles the silt of the defilements — and pakkhandana — leaping forward, like one who ventures across a flood (oghuttaraṇo viya, citing Sn 184's saddhā tarati oghaṃ). The pair marks faith's two poles: a stillness that lets the murk settle, and a courage that commits the body to the crossing. Without the first, the mind stays cloudy; without the second, clarity remains uncommitted. The Yogācāra cultivation chain begins here for the same reason: every later factor (will, resolve, mindfulness, concentration, wisdom) requires the stillness-and-venture that śraddhā provides as its foundation.
Trust — toward what is real (astitva), what is virtuous (guṇavattva), and what is attainable (śaktatva): to recognize firmly, to settle in serene clarity, and to incline with longing. This is its nature. To counter distrust, and to provide the basis on which zeal can arise: this is its function.
譯translator's note
譯者按： 結構分析詳 S3-P08。信（śrad-dhā）↔ 定（sam-ā-dhā，→#17）共 √dhā 根——別境五修習鏈之首尾兩環皆「置心」之動詞派生，是梵文形態學給出的 deep 架構。