誰知道grammar point · tier 1 · 誰知道… fronting an unforeseen outcome (who'd have thought…)
A rhetorical "who knew" set before an event that already happened, framing it as something nobody could have foreseen.
字源 FORM what the parts do
誰 asks who in words (言); 隹 only lends the sound. 知 is an arrow (矢) by a mouth (口), the answer that flies straight; 道 is the road (辶) the head (首) takes those words down. Put together, it asks who walked the road of knowing this in time, and the rhetorical who answers itself: nobody did.
故事 STORY a scene to remember it by
A face turns to a crowd and asks who saw this coming; every mouth stays shut, and the thing has already happened anyway.
字源自撰記憶法
框 · Frame
[clause A, the expected setup]，誰知道 [clause B, the surprising outcome]
觸 · Trigger
You want to report that something already happened against all expectation, and brush off the blame by saying nobody could have foreseen it.
序 · The move
1Lay down the ordinary setup first — the small or harmless thing that gave no warning.Does the first clause sound like nothing unusual was coming?
2Drop in 誰知道 as the turn, then state the outcome that already landed.Did the outcome actually happen? 誰知道 fronts a real result, not an open guess.
3Keep the answer unspoken — the rhetorical "who" stands for nobody, so the surprise carries itself.Are you reporting a shock you already know, not asking the listener to supply who knows?
例 · Examples
1才only just (barely begun)下了一個鐘頭one hour的雨，誰知道who'd have known家裡就then already淹水to flood了。
It had rained for barely an hour — who'd have thought the house would flood.
界 · Boundary
不知道… (embedded uncertainty)
不知道 reports a question still open to you, answer unknown and unsettled. 誰知道 fronts a fact already settled and surprising; its "who" is rhetorical and means nobody, not a real gap in what you know.
誰知道？ (a literal who-knows question)
As a genuine question (誰知道答案？— who knows the answer?) it asks the listener to name someone. As this pattern it asks nobody, takes no reply, and bends straight into the unforeseen outcome.
他病了，誰知道他好了沒有。 ✗ → 不知道他好了沒有。 ✓ (an open uncertainty you still hold uses 不知道, not 誰知道)
誰知道家裡淹水了嗎？ ✗ → 誰知道家裡就淹水了。 ✓ (誰知道 fronts a stated outcome, never closes with the question particle 嗎)
我以為沒事，誰知道。 ✗ → 我以為沒事，誰知道後來出事了。 ✓ (誰知道 must lead into the surprising result, not dangle alone)
English "who knows" can stay a live shrug about the future (who knows what'll happen). 誰知道 here points backward at something that already occurred, carrying "who would have thought" — keeping it future-facing misreads the pattern.