Who ever made up the equivalents of the Korean alphabet and the Roman alphabet, didn’t understand the Roman alphabet. On top of that, Korean has sounds we don’t have in English or in other languages that use the Roman alphabet. Still, another reason is because they have specific verb and adjective endings, and they have to make the verb endings fit. Also, some words are just written that way, and they are considered less hard. They feel like words that flow are kinder.
A good example of letters that don’t match well is 오 and 어. In English, both of these are simple a long “o.” They are pronounced slightly different, but it would just be the difference in accents in English, but not so in Korean. They make a different in the sounds, so they feel they need separate letters. 오 is transcribed in English as “o.” However, 어 is transcribe in English as “eo.” Initially, when I saw it is was extremely hard to wrap my head and my mouth around “eo.” I kept watched them as they spoke and when they used this letter, I realized they were rounding their mouth more for ‘어 (eo) than they were for 오 (o). I had to really concentrate hard to figure out the difference. However, to them, there is a big difference, and they wanted a way to represent it with our alphabet.
I will explain to you how they feel a word is kinder. For the word that is equivalent to “am, are, or is” to identify something, you can say it several different says. If you say 이습니다 (ee-sub-nee-dah), it is considered very formal. If you say 이다 (ee-dah), it is written on the page. If you say 이예요 (ee-ye-yo) with lots of vowels, it is considered a little less formal and even kinder because of the flow of the vowels. If you say 이야 (ee-ya), it is very informal, and you only use it with your best buddy or if you are being rude. If you say 이다 (ee-dah), people will think you are rather hard because it has that 다 (dah) and the vowels are not flowing like in 이예요 (ee-ye-yo) or 이야 (ee-ya).
Usually, in Korean, there are not actually two vowels together, but that is how they represent them in English letters trying to make the difference. The phonics system for the Roman or English letters is just not the same when they are writing Korean and if we are writing English, Spanish, or some other European language. If you are actually writing with the Korean letters, you can’t put two vowels together, but there are vowel combinations we can use in English and other European languages. If you are strictly using Korean letters, you have to have most words with every other letter a consonant and a vowel. They even change their post position particles according to what the last letter of the proceeding word is. An example of this is if your word ends in a consonant, and it is a subject, you can only use 이 (ee) or 은 (un.) However, if the subject ends in a vowel, you can only use 가 (gah) or 는 (nun).
When we represent 이 with “ee,” the first Korean letter is just a place holder. “ㅇ” has no sound at the beginning of a word, and “ㅣ” is only one letter, and it is what actually has the sound of “ee.” When you write, 어 (eo) in Korean, the first letter “ㅇ,” again, has no sound, and the “ㅓ” is only one letter, and it has the sound “eo.” We need two letters to represent it in Roman letters.
You see, when we see Korean written in Roman letters, it is just their approximation of the sound. If we were to really write it with English phonics, it wouldn’t be written that way at all. However, someone made up a different system for the sounds of the Roman letters in Korea. They also have the feeling that some words are rather harsh if there are too many consonants. In some ways, we may feel that in English. An example of this is something one of my professors said to me in graduate school. I wasn’t from Texas, but I was studying in Texas. I was used to pronouncing all the letters and not being sloppy about my language at all. However, one of my professors pulled me aside and suggested that I begin dropping the “g” off the end of the word when a word ended in “ing.” He told me it may help people feel more comfortable. It was a softer way of speaking. Korean has a softer way of speaking too, and that is putting that 요 (yo) on the end of their verbs.