pretty = 이쁘다, 예쁘다 (same meaning) Beautiful = 아름답다. 1. you are so beautiful = 당신 참 아름다워요 2. you are so pretty = 당신 참 예뻐요 (이뻐요 also ok) It's almost same. When you like picture, you will say "와... 이 그림 정말 예쁘다' (wow this picture is really pretty) or "와.. 이 그림 정말 아름답다' (wow this picture is really beautiful) Both will be OK. But in case of baby, it would be a little strange if you say "와~~ 이 아기 정말 아름답다" (Wow This baby is really beautiful), I guess english is also same. In case of above, "와~ 이 아기 정말 이쁘다" (wow this baby is really pretty) will be more natural. Because "이쁘다" " 예쁘다" (pretty) has some meaning of "cute" i think. '아름답다" (Beautiful) has...well...sort of mature feeling? just my opinion. ^__^