If you’ve learnt Japanese, you probably know the predicament I and many others face. We were taught the casual form of です is だ and that of でしょう is だろう, which is grammatically fine. Except that the nuance is really different―something I found out only after a number of years living here. I only realised it when a visiting friend used だろう in place of でしょう in a conversation with a Japanese friend who started laughing. It turns out, だろう isn’t exactly what we were taught it is.
でしょう is used, as you probably know, to be similar as the “right?” and “isn’t it?”or “doesn’t it?” in English. Such as when you’re unsure of something and you’d like to confirm it:
Or when you are surprised someone says something you like, such as chicken rice, doesn’t taste good and you want to assure yourself you heard them right:
But while だろう is indeed the closest casual replacement, it has a more confrontational nuance as “I told you, didn’t I?” and “see I’m right, right?” For example, you tell your friend the durian tastes good but they’re like “it stinks so bad, I don’t want to try.” But when they try it and falls in love with the fruit, you can go: おいしいだろう！