“〜hitori de ni・〜shizen to”: Naturally, On Its Own [JLPT N1]

Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026

「ドアがひとりでに開いた」「自然と上達する」 — it happens on its own, no one's doing it.

「ドアがひとりでに開いた」 — no one touched it, yet it moved by itself

To depict “no human intervention, yet it happens naturally／automatically,” 「誰も触っていないのに、ドアがひとりでに開いた」 (no one touched it, yet the door opened by itself) — 「〜ひとりでに・〜自然と」 = naturally, by itself, used to express “a state that occurs naturally (automatically) without human intervention.” This guide covers the emphasis difference between the two (one leans ‘an object by itself,' one leans ‘taking its natural course') and separates them from 「自動的に (a machine-set automatic).」

Core: without human effort, it just becomes so on its own

This set both expresses “occurs naturally (automatically) without human intervention,” but with different emphases:

① ひとりでに = by itself, automatically (no human intervention, an object/phenomenon “on its own” ～):

• 誰も押していないのに、ブザーがひとりでに鳴った (no one pressed it, yet the buzzer sounded by itself).
• 傷は放っておいても、ひとりでに治る (a wound heals by itself even if left alone).

② 自然と（自然に）= naturally, without realizing (taking its natural course):

• 練習を続けるうちに、自然と上達した (as I kept practicing, I naturally improved).
• 彼の話を聞いて、自然と涙があふれてきた (hearing his story, tears naturally welled up).

Feel: both are “happens naturally, without human effort,” but — 「ひとりでに」 leans “(without human effort) an object/phenomenon by itself ～” (a door opens itself, a fire goes out itself, a wound heals itself), with an “automatic, uncanny” flavor; 「自然と」 leans “(in the course of things) taking its natural course, without realizing ～” (naturally learning, smiling without noticing), broader, often for feelings, abilities, changes. In English: ひとりでに = “by itself, on its own”; 自然と = “naturally, without realizing.”

Attachment rules

See it in context

• 風もないのに、ろうそくの火がひとりでに消えた。(With no wind, the candle flame went out by itself.)
• 長く使っていると、設定がひとりでに元に戻ることがある。(With long use, settings sometimes revert by themselves.)
• 毎日繰り返すうちに、体が自然と動きを覚えた。(Repeating daily, my body naturally learned the movements.)
• その場にいると、自然と笑顔になる。(Being in that place, you naturally break into a smile.)
• 無理に忘れようとしなくても、時間がたてば自然と薄れていく。(Even without forcing yourself to forget, with time it naturally fades.)

⚠️ Common mistakes to avoid

① 「ひとりでに」 leans ‘an object/phenomenon by itself (no human effort)'; 「自然と」 leans ‘taking its natural course, without realizing.' This is the two's core emphasis difference. 「ひとりでに」 = by itself, automatically (no human intervention, stressing ‘an object/phenomenon ‘on its own' acting'): it stresses “no one touched it, no one did it, yet it ～ by itself,” with an “automatic, uncanny” flavor, mostly for objects', phenomena's automatic changes: ドアがひとりでに開いた (the door opened by itself — no one touched it), 機械がひとりでに止まった (the machine stopped by itself), 傷がひとりでに治る (a wound heals itself). 「自然と（自然に）」 = naturally, without realizing (taking its natural course, broader): it stresses “(in the course of things) following nature, without realizing, it just ～,” mostly for the gradual change of feelings, abilities, states of mind: 自然と上手になる (naturally get good), 自然と涙が出る (tears come naturally), 自然と仲良くなる (become close without realizing). Test: to say “(no human effort,) an object/phenomenon ～ by itself” (with an automatic feel) → ひとりでに; to say “taking its natural course, without realizing ～” (feelings/abilities/gradual change) → 自然と (see 〈自然に・自然と〉).

② Both are adverbs, modifying a naturally-occurring action／change. The attachment is simple — both are adverbs, placed directly before the action／change modified: ドアがひとりでに開く, 自然と笑顔になる. What they modify is “an action or change that occurs naturally/automatically (without human effort),” needing no particle. Mnemonic: ひとりでに／自然と ＋ (a naturally-occurring action/change).

③ Division of labor with 「自動的に (a machine-set automatic).」 These three all translate as “automatically,” but differ in feel. 「ひとりでに」 = (without external force) by itself, naturally (with an “uncanny, not-designed” automatic feel): ドアがひとりでに開いた (the door opened by itself — no one touched it, a bit eerie/uncanny). 「自動的に」 = automatically (a machine/system's ‘designed' automatic) (technical, human-designed automatic): ドアが自動的に開く (an automatic door opens automatically — designed that way), ライトが自動的に消える (the light goes off automatically — a sensor setting). Difference: 「ひとりでに」 is “(no human effort,) it ～ by itself” (with an uncanny feel, not designed); 「自動的に」 is “(a machine/system-set) automatic ～” (human-designed, technical). Test: to say “(no one touched/set it,) it ～ by itself” (uncanny automatic) → ひとりでに; to say “(a machine/system) automatically ～” (designed automatic) → 自動的に. E.g. 「電源がひとりでに切れた (the power went off by itself — no one turned it off, eerie)」 uses ひとりでに; 「省エネのため、画面が自動的に暗くなる (to save power, the screen dims automatically — a setting)」 uses 自動的に. One is “eerily by itself,” one is “a designed automatic.”

🔄 Compare: ひとりでに／自然と／自然に／自動的に

💡 The one thing to remember

「〜ひとりでに・〜自然と」 = naturally, by itself — three points: ① different emphases — 「ひとりでに」 leans “(no human effort) an object/phenomenon by itself ～” (the door opens itself, with an uncanny automatic feel); 「自然と」 leans “(in the course of things) taking its natural course, without realizing ～” (naturally learning, often feelings/abilities/gradual change, see 〈自然に・自然と〉); ② both are adverbs, placed directly before the action/change; ③ division of labor with 「自動的に (a machine-set automatic)」 — ひとりでに is “(no human effort,) it ～ by itself” (not designed), 自動的に is “(designed) automatic.” This set suits depicting that “without human effort, it just happened naturally/automatically” state — “the door opened itself,” “I learned it without realizing.” To stress “(no one touched it,) the object ～ by itself” use ひとりでに; to stress “taking its natural course, without realizing” use 自然と.

❓ Questions you might have

Q: Do 「ひとりでに」 and 「自然と」 mean the same? Interchangeable?

Close in meaning (both “happens naturally, without human effort”), but different emphases, not always interchangeable. 「ひとりでに」 = by itself, automatically (stressing ‘no human intervention, an object/phenomenon ‘on its own' acting'): its focus is “no one touched it, no one did it, yet it ～ by itself,” with an “automatic, even somewhat uncanny” flavor, mostly for objects', machines', physiological phenomena's automatic changes: ドアがひとりでに開いた (the door opened by itself — no one touched it), 涙がひとりでにこぼれた (tears spilled by themselves — involuntarily), 傷がひとりでにふさがる (a wound closes itself). It stresses the automaticity of “it ～ (just) by itself.” 「自然と（自然に）」 = naturally, without realizing (stressing ‘taking its natural course, gradually in the process'): its focus is “(in some process) following nature, without realizing, it just ～,” mostly for the gradual change of feelings, abilities, states of mind, relationships: 練習するうちに自然と上達する (practicing, you naturally improve), 自然と笑顔になる (naturally break into a smile), 時間がたてば自然と忘れる (with time you naturally forget). It stresses “taking its natural course, gradually without realizing ～.” Difference: 「ひとりでに」 leans “(no external force) an object/phenomenon acting by itself” (automatic, momentary, uncanny); 「自然と」 leans “(in a process) taking its natural course, gradual change without realizing” (gradual, often feelings/abilities). In some cases the two work (涙がひとりでに／自然と出る = tears come by themselves/naturally), but: to stress “(no one touched it,) an object/machine ～ by itself” → ひとりでに (automatic, uncanny); to stress “(in a process) without realizing, taking its natural course ～” (especially the gradual change of feelings/abilities) → 自然と. Test: subject is “an object/phenomenon, momentary automatic” → ひとりでに; subject is “a feeling/ability/relationship, gradual change” → 自然と (see 〈自然に・自然と〉).

Q: 「ひとりでに」 and 「自動的に」 both mean “automatically” — how do I tell them apart?

The difference is ‘whether it's a ‘human-designed' automatic.' 「ひとりでに」 = (no human effort, not designed) by itself, naturally (with an uncanny feel): it stresses “no human operation, and not designed that way, yet it ～ by itself,” often with a “inexplicable, uncanny, unexpected” flavor: 電源がひとりでに切れた (the power went off by itself — no one turned it off, inexplicably, eerie), パソコンがひとりでに再起動した (the PC restarted by itself — no operation, unexpected). Its “automatic” is “(no one did it,) it did it itself,” often a bit surprising or eerie. 「自動的に」 = (a machine/system-‘designed') automatic (technical, human-designed): it stresses “(designed, set to) operate automatically,” a human-designed, expected automatic: ドアが自動的に開く (an automatic door opens automatically — designed that way), データが自動的に保存される (data is saved automatically — a system setting), 電気が自動的に消える (the light goes off automatically — a sensor setting). Its “automatic” is “(designed,) the system/machine executes automatically,” an expected function. Difference: 「ひとりでに」 is “(no human effort, not designed) it ～ by itself” (uncanny, unexpected); 「自動的に」 is “(designed) automatic ～” (human-designed, an expected function). Test: to say “(no one touched/set it,) yet it ～ by itself” (surprising, uncanny) → ひとりでに; to say “(a machine/system designed to) automatically ～” (an expected function) → 自動的に. E.g. 「勝手にアプリがひとりでに開く (an app opens by itself — no tap, abnormal)」 uses ひとりでに (with a “how is this happening” abnormal feel); 「一定時間で自動的にログアウトされる (after a set time you're logged out automatically — a security setting)」 uses 自動的に (a normal function). One is “uncannily by itself,” one is “a designed automatic.”

🖊️ Practice Questions (5)

Q1. 「練習を重ねれば、___上達するものだ。」(naturally, of its own accord)

(A) 自然と　(B) 勝手に　(C) わざと　(D) むりに

Q2. 「ドアがひとりでに開いた」の意味は?

(A) The door opened by itself (no one touched it)

(B) Someone opened the door

(C) The door broke and won't open

(D) Deliberately opened the door

Q3. 「ひとりでに」と「勝手に」の違いは?

(A) ひとりでに = automatic/spontaneous (neutral); 勝手に = without permission (often negative)

(B) The two are exactly the same

(C) ひとりでに = without permission

(D) 勝手に = neutral/spontaneous

Q4. 「自然と」の後に来やすいのは?

(A) A spontaneous change (笑顔になる・身につく)

(B) Command

(C) Pure hypothesis

(D) Question

Q5. 用法が自然なのは?

(A) 傷が自然と治った。　(B) 自然とを食べる。

(C) ひとりでにだ高い。　(D) ひとりでに開けなさい(command)。

Answer Explanations

1. (A) 自然と ── naturally improves.

2. (A) ── the door opened by itself.

3. (A) ── ひとりでに is neutral/spontaneous; 勝手に is 'without permission' (negative).

4. (A) ── followed by a spontaneous change.

5. (A) ── 「傷が自然と治った」 is correct.