What it means
دلیل (dalil) is a reason, a cause, a piece of evidence. The word does double duty. In everyday conversation it means the reason you did something: چرا نیومدی؟ دلیلت چی بود؟ (cherā nayumadi? dalilet chi bud, why didn’t you come? what was your reason?). In legal, academic, or argumentative contexts it means evidence, the thing you bring to prove a claim: دلیلت چیه که میگی این درسته؟ (dalilet chiye ke migi in doroste, what’s your evidence that this is right?).
The plural دلایل (dalāyel, reasons, evidence) takes an Arabic broken plural form and shows up in formal writing constantly: دلایل اقتصادی (dalāyel-e eqtesādi, economic reasons), دلایل کافی (dalāyel-e kāfi, sufficient evidence).
How to use it
The most common frames: به دلیل (be dalil-e, due to, because of), بیدلیل (bi-dalil, without reason), and دلیل دارد (dalil dārad, there is a reason). Persian uses به دلیل + noun where English would use “because of” + noun, and uses چون (chun, because) or به این دلیل که (be in dalil ke, for the reason that) for full clauses.
be dalil-e bārān, mashin nayāvardam.
Due to the rain, I didn’t bring the car.
به دلیل باران، ماشین نیاوردم.
bi-dalil narāhat nasho.
Don’t get upset for no reason.
بیدلیل ناراحت نشو.
dalil-e asli-ye estefā-ash maʿlum nist.
The main reason for his resignation is unclear.
دلیل اصلی استعفایش معلوم نیست.
Dalil vs ellat
Persian has a near-synonym, علت (ellat, cause), also Arabic in origin. The two overlap heavily and most speakers swap them freely. The technical distinction in classical philosophy: ellat is the metaphysical cause, the thing that makes something happen; dalil is the epistemic ground, the thing that proves something is true. In everyday speech this collapses. In academic and legal Persian, ellat tilts toward causation and dalil toward justification.
Where it comes from
Dalil is Arabic, from the root d-l-l (د-ل-ل), which means to guide, to point out, to indicate. The noun دَلِيل (dalīl) literally means “that which guides,” and in Arabic it also means a guide, a leader, a proof. Persian borrowed it during the early Islamic period and kept both senses, with the “evidence/reason” meaning becoming dominant.
References
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