I was wondering if you could silence summoner spells cause it seems like you can but sometimes you can't.
It all depends, the summoner spell cleanse can always be cast, even when stunned. The rest of them are stopped on Silence, Stun, Charm and Fear. But aren't stopped when your snared meaning you can't move but can still use your abilities and spells.
Edit: Except Flash, you can't use Flash while snared just as Patrick Stalder noted.