於grammar point · tier 3 · locative/temporal 於 (formal: sited at a place or time)
· yú
Formal preposition that wedges after the verb (or its auxiliary) to name the place or time an action is sited at; the written-register counterpart of 在.
字源 FORM what the parts do
於 is a worn crow-graph, the same bird as 烏, hired out as the empty joint of the sentence: at, in, on. It carries no place of its own; it takes the place or time set right behind it and pins the verb to that spot. The slot is its whole job.
故事 STORY a scene to remember it by
A verb hangs in the air, and 於 reaches behind it for the one spot named there; the action drops onto that spot and holds.
字源自撰記憶法
框 · Frame
[subj] (將/可) [verb] 於 [place / time]
觸 · Trigger
You are placing an action at a venue or a date in formal or written speech, and want the location to trail the verb the way an announcement reads.
序 · The move
1Name the verb of the event, then the place or time it lands on.Is what follows 於 a venue or a point in time, the spot the action is sited at? If it is a person being compared or a source the verb flows from, that is the other 於, not this one.
2Set 於 directly after the verb (or after its auxiliary 將/可), then the place or time.於 trails the verb; the place sits behind 於, never ahead of the verb the way 在 fronts it (在會議中心舉行 vs 舉行於會議中心 / 將於會議中心舉行).
3Keep the register formal — announcement, notice, report.Would 在 sound right in everyday speech here? If the line is casual, 在 is the plain word; 於 is the written dress.
例 · Examples
1本活動běn huódòng — this event將jiāng — will (formal future)於yú — at, in (formal)國際會議中心舉行jǔxíng — to hold (an event)。
This event will be held at the International Conference Center.
Same job, opposite seat and register. 在 fronts the place before the verb in plain speech (在會議中心舉行); 於 trails the verb in formal writing (舉行於 / 將於…舉行). Spoken-front vs written-trail.
Same graph, different load. 於1 follows an adjective or verb to mark a yardstick or origin (大於 larger than, 來自於 comes from). 於2 names where or when an event is sited. Compared-against vs sited-at.
✗ 本活動將在國際會議中心舉行於。 → ✓ 本活動將於國際會議中心舉行。 (於 wedges in before the place, not stranded at the end)
✗ 本活動將舉行在國際會議中心。 → ✓ 本活動將於國際會議中心舉行。 (formal register wants 將於…舉行, not a trailing 在)
✗ 會議於明天開始在台北。 → ✓ 會議將於明天在台北開始。 (one 於 per slot; the place takes its own marker, here 在 in plain position)
English 'at/in/on' always trails the verb ('held at the center'), so learners drop 於 in everyday Chinese where 在 fronts the place. 於 belongs to formal writing only; in speech the place goes before the verb with 在.