居然grammar point · tier 1 · stance adverb 居然 (and yet — astonished the fact stands against its buildup)
Pre-verbal stance adverb marking the stated fact as true and confirmed yet running against everything the buildup predicted — astonishment that it is so.
字源 FORM what the parts do
然 is the grammar particle: fire (灬) under 肰 for the sound, the blaze borrowed long ago for so and thus, then worn to the look of how a thing stands — the 然 of 忽然, 顯然. 居 is along for the sound, its dwell-and-stay sense set aside here. The pair sits before the verb and marks the fact it heads as standing real, square against everything the run-up leaned toward.
故事 STORY a scene to remember it by
Everything leading in tilts the same way, one outcome owed. The next fact lands hard against that tilt and stays standing — the wider the gap it crossed, the more it holds.
字源記憶法
框 · Frame
[buildup leaning one way] ，[subj] 居然 [verb / fact running against it]
觸 · Trigger
What the situation set you up to expect did not hold, and the thing that did hold is real and surprising — you flag the gap between the buildup and the fact.
序 · The move
1Lay out the buildup that leans toward one expected outcome.Does the run-up genuinely owe a different result, so the fact can land against it?
2Drop 居然 right before the verb of the fact that defies it.居然 sits inside the clause before the predicate, not at the clause head like a conjunction.
3Let the predicate state the surprising fact as plain truth.Read it back: it reports something real that happened, not a guess or a wish. If it could be a prediction, 居然 is wrong.
卻 marks a plain contrast: the predicate runs counter to the setup, no surprise loaded. 居然 carries the astonishment — the fact crossed a gap it had no business crossing. 外面太陽很大，溫度卻很低 states a mismatch; swap in 居然 and it becomes a shock that it is so.
竟然 is the near-twin in the same pre-verb slot, leaning toward outright disbelief and harder tone. 居然 carries the same against-the-buildup surprise a touch more measured; they trade in most sentences.
雖然…但是… frames a concession from both ends — granted X, still Y — and predicts the turn. 居然 marks no concession: the fact arrives unframed and the surprise is that it stands at all.
✗ 居然他還有時間寫小說。 → ✓ 他居然還有時間寫小說。 (居然 sits after the subject, before the verb, not at the clause head)
✗ 他工作很忙，他居然可能有時間。 → ✓ 他工作很忙，居然有時間。 (居然 reports a real fact, not a guess — drop the maybe)
✗ 他工作很忙，但是有時間。 → ✓ 他工作很忙，居然有時間。 (但是 only joins clauses; 居然 loads the astonishment onto the predicate)
English carries this with 'and yet' or 'of all things' floated to the clause front; learners front 居然 the same way. 居然 stays buried after the subject, on the predicate.