Can you cast a sorcery during your main phase if the stack is empty but your opponent has a triggered ability waiting to go on the stack?

Casting a sorcery requires that it be your main phase, the stack is empty, and you have priority (CR 307.1). The question is whether a triggered ability that has triggered but not yet been placed on the stack violates the 'stack is empty' condition — and it does not.

According to CR 603.3, triggered abilities go on the stack the next time a player would receive priority. Until that moment arrives, the ability exists in a kind of 'pending' state but is not yet on the stack. Therefore, the stack is still technically empty in the interim.

However, in practice, the moment you or your opponent would receive priority, all pending triggered abilities are placed onto the stack first (CR 117.5). This means that as soon as either player gets priority, those triggers land on the stack before anyone can act — so you'll need to deal with them before the stack is empty again.

Concrete example: It's your main phase. Your opponent controls a Sunken Hope (which triggers at the beginning of each upkeep). If it triggers during your upkeep, that trigger is pending. You cannot shortcut straight to casting a sorcery — once priority is about to be granted, the trigger goes on the stack first, and both players must pass priority with the stack empty before you can cast your sorcery.

So while the stack is technically empty before triggers are placed, you will never actually receive priority with the stack empty while triggers are pending — they always get placed first. In effect, you must resolve all pending triggers before casting your sorcery.