सिद्धांत (siddhaant)

noun A learned, formal noun covering 'principle' (a rule one lives or acts by) and 'theory/doctrine' (a systematic set of ideas, as in science or philosophy) -- both senses come from the same root idea of an established, settled truth.
Sense 1 : a personal or moral rule one adheres to
noun, masculine
Synonyms: नियम (niyam), उसूल (usool)
Frequency: high
Cultural Note: You will often hear सिद्धांतवादी (siddhaantvaadii, 'a person of principle') used respectfully about someone who sticks to their values even at personal cost -- a certain old-school Delhi uncle who won't cut a corner even in traffic is exactly this type. It pairs naturally with जीवन के सिद्धांत (jiivan ke siddhaant, 'principles of life'), a common phrase in advice-giving and obituaries alike.
Common Mistakes: 1) Learners often reach for नियम (niyam) here, which works for rules in general (traffic rules, game rules), while सिद्धांत (siddhaant) is reserved for a person's own guiding belief or code of conduct -- e.g. someone who refuses bribes 'on principle.' 2) It is frequently used with पर (par) in the phrase सिद्धांतों पर चलना (siddhaanton par chalnaa, 'to live/act by one's principles'), not with से (se).
Sample Sentences:
मेरे जीवन का एक सिद्धांत है कि झूठ कभी नहीं बोलना चाहिए। It is a principle of my life that one should never tell a lie.
(mere jiivan kaa ek siddhaant hai ki jhooth kabhii nahiin bolnaa chaahie।)
Register: Neutral -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
वे अपने सिद्धांतों पर कभी समझौता नहीं करते। He never compromises on his principles.
(ve apne siddhaanton par kabhii samjhautaa nahiin karte।)
Register: Neutral -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
शर्मा जी सच में सिद्धांतवादी आदमी हैं, ट्रैफिक में भी लाल बत्ती पार नहीं करते। Sharma ji is truly a man of principle -- he won't even jump a red light in traffic.
(sharmaa jii sach men siddhaantvaadii aadmii hain, traiphik men bhii laal battii paar nahiin karte।)
Register: Casual -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
उन्होंने अपने जीवन के सिद्धांतों को कभी नहीं छोड़ा। He never abandoned his life's principles.
(unhonne apne jiivan ke siddhaanton ko kabhii nahiin chhodaa।)
Register: Neutral -- Mood: Indicative -- Aspect: Perfective -- Tense: Past -- Voice: Active
काश मैं भी अपने सिद्धांतों पर उतना ही अडिग रह पाता। I wish I too could stay as firm on my principles.
(kaash main bhii apne siddhaanton par utnaa hii adig rah paataa।)
Register: Neutral -- Mood: Counterfactual -- Aspect: Habitual -- Voice: Active
अपने सिद्धांतों से मत डिगो, चाहे कुछ भी हो जाए। Don't waver from your principles, no matter what happens.
(apne siddhaanton se mat digo, chaahe kuchh bhii ho jaae।)
Register: Neutral -- Mood: Imperative -- Voice: Active
स्वर्गीय शर्मा जी अपने जीवन के सिद्धांतों के लिए हमेशा याद किए जाएंगे। The late Sharma ji will always be remembered for the principles of his life.
(svargiiy sharmaa jii apne jiivan ke siddhaanton ke lie hameshaa yaad kie jaaenge।)
Register: Formal -- Mood: Indicative -- Tense: Future -- Voice: Passive
अगर तुम अपने सिद्धांत बदलते रहोगे, तो लोग तुम पर भरोसा नहीं करेंगे। If you keep changing your principles, people won't trust you.
(agar tum apne siddhaant badalte rahoge, to log tum par bharosaa nahiin karenge।)
Register: Neutral -- Mood: Indicative -- Tense: Future -- Voice: Active
क्या यह उचित है कि पैसे के लिए अपने सिद्धांत बेच दिए जाएं? Is it right that one's principles should be sold for money?
(kyaa yah uchit hai ki paise ke lie apne siddhaant bech die jaaen?)
Register: Formal -- Mood: Subjunctive -- Tense: Present -- Voice: Passive
मैं चाहता हूँ कि मेरे बच्चे भी ईमानदारी को अपना सिद्धांत बनाएं। I want my children to also make honesty their principle.
(main chaahtaa hoon ki mere bachche bhii iimaandaarii ko apnaa siddhaant banaaen।)
Register: Neutral -- Mood: Subjunctive -- Tense: Present -- Voice: Active
उसका सिद्धांत था कि दूसरों की मदद बिना किसी लालच के करनी चाहिए। His principle was that one should help others without any greed.
(uskaa siddhaant thaa ki doosron kii madad binaa kisii laalach ke karnii chaahie।)
Register: Literary -- Mood: Indicative -- Tense: Past -- Voice: Active
Sense 2 : a systematic theory or doctrine
noun, masculine
Synonyms: थियोरी (thiyorii, colloquial, English loanword), मत (mat, meaning scope: doctrine/opinion)
Frequency: medium
Cultural Note: This is the word you will meet in school textbooks and news reports on science or economics -- गुरुत्वाकर्षण का सिद्धांत (gurutvaakarshan kaa siddhaant, 'the theory of gravity') is a staple phrase from physics class. It carries the same weight and formality as English 'theory' or 'doctrine,' so it feels out of place in casual chat about, say, a friend's pet theory about traffic.
Common Mistakes: 1) In science and academic contexts, सिद्धांत (siddhaant) is the standard word for 'theory' (e.g. सापेक्षता का सिद्धांत (saapekshtaa kaa siddhaant, 'theory of relativity')) -- learners who default to the English loanword थियोरी (thiyorii) sound casual rather than academic.
Sample Sentences:
गुरुत्वाकर्षण का सिद्धांत न्यूटन ने प्रतिपादित किया था। The theory of gravity was propounded by Newton.
(gurutvaakarshan kaa siddhaant nyootan ne pratipaadit kiyaa thaa।)
Register: Formal -- Mood: Indicative -- Aspect: Perfective -- Tense: Past -- Voice: Active
यह सिद्धांत डार्विन के विकासवाद पर आधारित है। This theory is based on Darwin's theory of evolution.
(yah siddhaant daarvin ke vikaasvaad par aadhaarit hai।)
Register: Formal -- Mood: Indicative -- Tense: Present -- Voice: Active
अर्थशास्त्र की कक्षा में मांग और आपूर्ति के सिद्धांत को अच्छी तरह समझाया गया। In the economics class, the theory of demand and supply was explained well.
(arthshaastr kii kakshaa men maang aur aapoorti ke siddhaant ko achchhii tarah samjhaayaa gayaa।)
Register: Formal -- Mood: Indicative -- Aspect: Perfective -- Tense: Past -- Voice: Passive
वैज्ञानिक इस सिद्धांत की परीक्षा करते रहे हैं। Scientists have been testing this theory.
(vaigyaanik is siddhaant kii pariikshaa karte rahe hain।)
Register: Formal -- Mood: Indicative -- Aspect: Continuous -- Tense: Present -- Voice: Active
अगर यह सिद्धांत सही होता, तो प्रयोग के नतीजे अलग होते। If this theory were correct, the experiment's results would have been different.
(agar yah siddhaant sahii hotaa, to prayog ke natiije alag hote।)
Register: Formal -- Mood: Counterfactual -- Aspect: Habitual -- Voice: Active
छात्रों को सापेक्षता के सिद्धांत के बारे में विस्तार से पढ़ाया जाएगा। Students will be taught about the theory of relativity in detail.
(chhaatron ko saapekshtaa ke siddhaant ke baare men vistaar se padhaayaa jaaegaa।)
Register: Formal -- Mood: Indicative -- Tense: Future -- Voice: Passive
क्या तुम इस सिद्धांत को सरल शब्दों में समझा सकते हो? Can you explain this theory in simple words?
(kyaa tum is siddhaant ko saral shabdon men samjhaa sakte ho?)
Register: Neutral -- Mood: Indicative -- Aspect: Habitual -- Tense: Present -- Voice: Active
यह जरूरी नहीं कि हर नया सिद्धांत पुराने को गलत साबित करे। It is not necessary that every new theory prove the old one wrong.
(yah jaroorii nahiin ki har nayaa siddhaant puraane ko galat saabit kare।)
Register: Formal -- Mood: Subjunctive -- Voice: Active
पाठ्यपुस्तक में परमाणु संरचना के सिद्धांत पर एक पूरा अध्याय है। There is a whole chapter on the theory of atomic structure in the textbook.
(paathypustak men parmaanu sanrachnaa ke siddhaant par ek pooraa adhyaay hai।)
Register: Neutral -- Mood: Indicative -- Tense: Present -- Voice: Active
उस समय तक वैज्ञानिकों ने विकास का सिद्धांत पूरी तरह विकसित कर लिया था। By that time, scientists had fully developed the theory of evolution.
(us samay tak vaigyaanikon ne vikaas kaa siddhaant poorii tarah viksit kar liyaa thaa।)
Register: Formal -- Mood: Indicative -- Aspect: Perfective -- Tense: Past -- Voice: Active
Morphology
Noun
(sg.m.direct): सिद्धांत (siddhaant)
(sg.m.oblique): सिद्धांत (siddhaant)
(pl.m.direct): सिद्धांत (siddhaant)
(pl.m.oblique): सिद्धांतों (siddhaanton)