由grammar point · tier 1 · agent marker 由 (the act is done BY this party)
· yóu
Names the party an action sets out from: the one who carries it out and answers for it.
字源 FORM what the parts do
A closed 田-shape with one stem rising through the top. The word it writes is the source: where a thing sets out from. Read of an action, that source is the party it issues from.
故事 STORY a scene to remember it by
A shoot breaks the soil at one marked spot; every leaf above traces back to that root.
字源記憶法自撰
框 · Frame
[event/task] 由 [agent] [verb (+ object)]
觸 · Trigger
Pin who carries out a task and answers for it, in a formal or arranged setting.
序 · The move
1Put the task or event first as the topic.Is the thing being handled stated up front?
2Place 由 + the responsible party right after it.Does the slot after 由 name WHO acts, not what is acted on?
3Close with the verb the party performs.Could you answer 'who does this?' with the 由-phrase alone?
例 · Examples
1抽獎活動lucky-draw event將will (formal future)由by / carried out by電腦computer (the agent)選出select out得獎者prize-winner。
The winner of the lucky draw will be selected by a computer.
由 names the agent as the responsible source, neutral and often arranged or official. 被 spotlights the thing acted on, frequently something it suffers. Success: 由 answers 'who handles it'; failure: using 由 to report an injury done to a victim.
把 disposes of a definite object: the subject acts on it. 由 assigns the doing to a party: it answers who acts. Success: 由 fills the agent slot; failure: putting the object, not the agent, after 由.
✗ 由這個問題解決了。 → ✓ 這個問題由我們解決。 (the slot after 由 is the agent, not the thing handled)
✗ 晚餐由餐廳。 → ✓ 晚餐由餐廳準備。 (a verb must follow; 由 + agent alone is incomplete)
English 'by' marks the agent in a passive ('selected by a computer'), so learners reach for 被. 由 is the assignment reading of 'by' — who is put in charge — and stays neutral, unlike adversity-leaning 被.