From Jonathan Gardner's Korean Notebook
Glue is a vowel added to the Verb Stem of a verb to bring it into a new form. This is represented as "-어".
The best way to learn this is to start with -어. Then apply one or more of these rules, if applicable.
- If the word ends with an 어 sound, or one of the vowels that end with 어 (ie, 여, 에, 예, 워, 웨), then you don't have to do anything. The 어 sound is already accounted for.
- If the word ends with an 아 or 오 sound (ie, 아, 야, 애, 얘, 오, 요, 와, 왜), then you add an 아. Like the previous rule, the vowel will "roll into" the previous 아 if the vowel ends with that (ie, anything but 오 and 요).
- If the word is "하" from "하다", or any of the bazillion verbs that end in "하다", then you add "여". This is usually contracted down from "하여" to just "해". You'll only see "하여" in very formal or old-style speaking.
- If the word is "이다", then you have "야" instead.
- If the word is one of the "-렇다" verbs, then you change "렇" to "래". So, 그렇다 → 그래, etc...
- If the word ends with ㅂ and follows the ㅂ 불규칙 rule, then you drop the ㅂ and add "워".
- If the word ends with ㅅ and follows the ㅅ 불규칙 rule, then you drop the ㅅ and add "어".
- If the word ends with 르 and follows the ㄹ 불규칙 rule, then you drop the 르 and add "ㄹ러" or "ㄹ라", depending on whether the vowel before the 르 is 오/아 or something else.
- There are some other 불규칙 rules, but they are rare so you only need to know them if you know the word that follows the rule.
This really isn't that hard. Once you get the hang of it, it will make a ton of sense, and you'll wonder why you ever thought it could ever be any other way.
As a Conjunctive Ending, this means "and". It's a very, very tight and, usually meaning that two things are happening at once in the same action. But sometimes it means something happens, and then immediately later something else happens.
As an Final Ending, it is informal impolite. You use it towards children or close friends. It can mean a statement ("I am here"), to a question ("Where am I?") to a command ("be here.")
As an Incomplete Ending, it joins the two action verbs together in one, with the second action generally clarifying intent or direction.