Counterbalance + City of Solitude

[GreenOne]

Can the opponent use counterbalance in my turn if i have a city of solitude in play?

Here's what is said about City of Solitude:
Does not stop triggered abilities from being put on the stack. They are never "played". [D'Angelo 1999/07/01]

Is that true even if the triggered says "you may"?

[Brushwagg]

Short answer is yes your opponent can use Counterbalance's effect on your turn under City. The you may part is optional, so your opponent has to choose if they want to use it or not, it doesn't happen automatically.

[Tacosnape]

The longer answer is that the "You may" is a choice made upon resolution of the triggered ability and that it has nothing to do whatsoever with the Counterbalance trigger going on the stack.

Here's what happens.

1. You have a City of Solitude in play, your opponent has Counterbalance in play. It's your turn, you play a spell. Your spell goes on the stack.

2. Since the "You play a spell" part satisfies the trigger condition of Counterbalance that says "Whenever an opponent plays a spell," Counterbalance's trigger goes on the stack.

3. Assuming nobody responds to the Counterbalance trigger (Your opponent can't use Sensei's Divining Top, thanks to City of Solitude), it will resolve. On resolution, the opponent may choose to reveal the card and attempt to counter the spell.