至於grammar point · tier 1 · topic shift 至於 X (as for X, turning to the next matter)
Sets the matter just spoken of to rest and turns the attention onward to a second, related matter named right after it.
字源 FORM what the parts do
至 is something coming down onto the ground line (一) and stopping there — arrived, and at arrival's far edge, as far as it reaches. 於 is a worn crow-graph hired out as the empty joint of the sentence, at, in, to. The pair carries the attention onward and sets it down on the next matter named after them.
故事 STORY a scene to remember it by
One matter is laid to rest, and the attention travels on and comes down on the next one waiting beside it.
字源自撰記憶法
框 · Frame
[first matter, stated/settled]，至於 [second matter]，[remark about it]
觸 · Trigger
You have dealt with one matter and want to move the attention onto a second, related one and address it in turn.
序 · The move
1State or settle the first matter, so there is something already on the table to turn away from.Is there a prior matter the listener already has in view? 至於 turns FROM a matter just dealt with; with nothing before it, you want 關於 to open a topic from cold.
2Put 至於 + the second matter at the head of the next clause, with a pause after the matter.Is the new matter a different, related sub-topic, not the same line pushed further? For pushing the same line to its extreme case, reach for 甚至.
3Deliver the remark about the second matter.Does what follows genuinely treat the matter named after 至於, leaving the first matter behind?
例 · Examples
1開會to hold a meeting的時間time必須must, have to延期to postpone，至於zhìyú — as for, turning to the next matter延到postponed until什麼時候when, what time會再通知will notify again。
The meeting time has to be postponed; as for when it will be put off to, we will notify you again.
關於 opens a piece on a topic from cold, with nothing required before it (關於這件事，…). 至於 needs a first matter already settled to turn AWAY from, and shifts the attention onto a second one. Open-from-cold against turn-onward.
對於 names the TARGET an attitude or action is aimed at (對於這件事，我很生氣). 至於 marks a SHIFT to a new sub-topic to address next, no attitude built in. Aimed-at against moved-onto.
甚至 pushes the SAME line out to its most extreme case (…甚至連睡覺都開燈). 至於 switches to a DIFFERENT, related matter and takes it up in turn. Same line further against a different line started.
✗ 至於這次旅行，我們先說一下行程 (no prior matter to turn from) → ✓ 關於這次旅行，我們先說一下行程
✗ 他很努力，至於連假日都加班 (pushing the same line to its extreme) → ✓ 他很努力，甚至連假日都加班
✗ 時間延期了，至於什麼時候不知道 (no pause, comment fused to the matter) → ✓ 時間延期了，至於什麼時候，還不知道
English 'as for / as to' is a loose front tag that can open a topic cold; learners drop 至於 in that opening slot. 至於 only turns onto a SECOND matter after a first is already on the table — the cold-open belongs to 關於.