…because some thoughts are worth remembering
Reprimand in person (in private). Praise in writing.
The expanded version: When you reprimand in person, you can read their reactions, you give them an opportunity to respond or ask questions, and it can be informal. There is a place for written reprimands (e.g., documenting abuse for legal purposes) but I’ve seen too many managers give written reprimands as a way to avoid their fear of conflict. Praise in writing, so they can remember, and they know you mean it.