In Korean, ending consonants are not pronounced as clearly as they would be in the beginning of a word. This results in there being only 7 ending sounds for consonants. Originally more of the consonants have had “separate” pronunciations, but in modern Korean, the sounds have effectively merged together for certain consonants.
This is known as the 7 ending sounds rule.
Here are the ending consonants combined with the randomly chosen 가.
[ ] signifies pronunciation.
1. [각] = [갘]
3. [갓] = [갇] = [갖] = [갗] = [같] = [갛]
6. [갑] = [갚]
For each of the seven points above, the first ending mentioned is the “dominant” ending. That means, if you see the ending consonant -ㅊ it is effectively pronounced the same way as a word ending with -ㅅ. Therefore if -ㅊ is followed by e.g. -이에요 the combination will be pronounced “-시에요” because the ㅅ-sound replaces -ㅊ and then combines with -이에요.
In Korean each letter of the alphabet has a name. If we are to take the different consonants and say “it’s …” the following happens:
“ㄱ 이에요” = 기억이에요
“ㄴ 이에요” = 니은이에요
“ㄷ 이에요” = 디귿이에요 ~ 디긋이에요 => [디그시에요]
“ㄹ 이에요” = 리을이에요
“ㅁ 이에요” = 미음이에요
“ㅂ 이에요” = 비읍이에요
“ㅅ 이에요” = 시옷이에요
“ㅇ 이에요” = 이응이에요
“ㅈ 이에요” = 지읒이에요 ~ 지읏이에요 => [지으시에요]
“ㅊ 이에요” = 치읓이에요 ~ 치읏이에요 => [치으시에요]
“ㅋ 이에요” = 키읔이에요 ~ 키윽이에요 => [키으기에요]
“ㅌ 이에요” = 티읕이에요 ~ 티읏이에요 => [티으시에요]
“ㅍ 이에요” = 피읖이에요 ~ 피읍이에요 => [피으비에요]
“ㅎ 이에요” = 히읗이에요 ~ 히읏이에요 => [히으시에요]
“ㄲ 이에요” = 쌍기억이에요
“ㄸ 이에요” = 쌍디귿이에요 ~ 쌍디긋이에요 => [쌍디그시에요]
“ㅃ 이에요” = 쌍비읍이에요
“ㅆ 이에요” = 쌍시옷이에요
“ㅉ 이에요” = 쌍지읒이에요 ~ 쌍지읏이에요 => [쌍지으시에요]