1. to reason or use one's mind in a logical and coherent way, free from confusion or distraction
I need to think clearly before making this important decision.
Preciso pensar com clareza antes de tomar essa decisão importante.
2. to have a clear and focused mind without mental fog or muddled thoughts
It's hard to think clearly when you haven't slept well.
É difícil pensar com clareza quando você não dormiu bem.