percebesses

form-of imperfect second-person singular subjunctive

perceber の二人称単数不完了接続法

English Meaning

second-person singular imperfect subjunctive of perceber

Se percebesses as nuances da situação, saberias agir de forma mais apropriada.

もし状況の微妙な点に気づいていたら、より適切に行動できたでしょう。

If you had noticed the nuances of the situation, you would know how to act more appropriately.