Can I use 虽然 without 但是?
Yes, 虽然 can stand alone — but it can never pair with 所以.
虽然 is a flag that says a twist is coming. Your listener waits for the payoff, and 但是 is the natural one. You can skip it, and real people do: 虽然贵,我还是买了. What actually breaks the sentence is 所以. 因为……所以…… means cause and effect; 虽然……但是…… is a left turn. Mixing the two makes native ears trip.
| Situation / Pattern | Formula | Natural | Avoid |
|---|---|---|---|
| Textbook pair | 虽然 A,但是 B | 虽然贵,但是好用。 | 虽然贵,所以好用。 |
| Second half dropped | 虽然 A,B | 虽然贵,我还是买了。 | 虽然贵,所以我买了。 |
| First half dropped, very common in chat | A,但是 B | 贵是贵,但是好用。 | 贵是贵,所以好用。 |