Vowels and consonants consists a syllable and each syllable must have at least one vowel. The letter forms are as follows; ① vowel ② vowel + consonant, ③ consonant + vowel, ④ consonant + vowel + consonant. (cf. We don't count 'ㅇ' as a vowel when it comes at the first part of a letter.)
① (O) + 'ㅑ' = '야' , (O) + 'ㅗ' = '오', ② '앗' , '운', ③ '가', '소', ④ '밥', '콩'