The Turn You Didn't See Coming
ところが opens a new sentence and reports that what actually happened defied the setup.
- 晴れる予定でした。ところが大雨になりました。(It was supposed to be clear. But then it poured.)
It Reports, It Doesn't Judge
The second clause must be a fact that happened, not an opinion, a plan or a request:
| ○ ところが誰も来なかった | a fact |
| × ところが行きましょう | a suggestion |
| × ところが行ってください | a request |
This is what separates it from でも and しかし, which take anything.
Against ところで
One character apart, unrelated:
| Pattern | Meaning |
|---|---|
| ところが | however — an unexpected result |
| ところで | by the way — a change of topic |
Against のに
のに joins two clauses inside one sentence. ところが starts a new one. The contrast is the same; the packaging differs, and ところが gives the turn more weight because the reader has already finished the first thought.