Eu vi um pouco de pizza na cozinha. Não sei se tem sobrando. Alguém talvez tenha comido toda pizza.
I saw some pizza in the kitchen earlier. I don’t know if there’s any left. (eat) → Someone MAY/ MIGHT HAVE EATEN all the pizza.
Gary não esta na reunião porque eu esqueci de avisar ele. Ele não tinha como saber que estamos aqui.
3. Gary isn’t here in the meeting because I forgot to tell him about it. (know) → He COULDN'T HAVE KNOWN we are here
Eu não sabia que ia chover. Se eu soubesse eu teria trazido um guarda-chuva
I didn’t know it was going to rain. If I had known it was going to rain, I COULD/ WOULD have brought my umbrella.