LEARN KOREAN (한국어) [GRAMMAR] #1

VERBS

Present Tense

When the last syllable of the stem ends in a consonant, you add 는다 to the stem of the word:

먹다 = 먹는다 - to eat (먹 + 는다)
닫다 = 닫는다 - to close (닫 + 는다)

Examples:
나는 밥을 먹는다 - I eat rice
나는 문을 닫는다 - I close the door

When the last syllable of the stem ends in a vowel, you add ㄴ to the last syllable followed by 다

배우다 = 배운다 - to learn (배우 + ㄴ다)
이해하다 = 이해한다 - to understand (이해하 + ㄴ다)
가다 = 간다 - to go (가 + ㄴ다)

Examples:
나는 그것을 이해한다 - I understand that
나는 한국어를 배운다 - I learn Korean
나는 집에 간다 - I go home

Past tense

Before you learn this, you need to know something important. Korean grammar is based on adding things directly to verbs or adjectives to create a specific meaning. For example, you saw how 는다 or ㄴ다 can be added to the stem of a verb in order to conjugate that verb to the present tense.

Hundreds of grammatical principles (not just conjugations, but grammatical principles that have actual meanings in sentences) are created by adding certain things to the stems of verbs and adjectives. For example, the following is a short list of additions that can be added to the stems of verbs and/or adjectives to create a specific meaning:
• 기 to create a noun form of a verb or adjective
• 아/어서 to give reason
• (으)시 to denote an honorific acting agent
• 자 to make a suggestion
• 아/어야 한다 to indicate that one must do something
•ㄴ/는다고 to quote somebody
The list could go on and forever.

Notice that some of these grammatical principles require the addition of 아/어. Many grammatical principles (or conjugations, or any other thing) require the addition of 아/어 to the stem of a verb or adjective. Notice that the "slash" indicates that you need to choose what actually gets added to the stem. In some cases it is 아, and in some cases it is 어. The following is the rule that you can use to determine if you should add 아 or 어:
• If the last vowel in a stem is ㅏ or ㅗ (this includes rare cases of the last vowel being ㅑ or ㅛ) you add 아 followed by the remainder of the grammatical principle. (The only exception is 하. If the last syllable in a stem is 하, 여 must be added to the stem followed by the remainder of the grammatical principle instead of 아).
• If the last vowel in a stem is anything but ㅏ or ㅗ you add 어 followed by the remainder of the grammatical principle.

When conjugating to the past tense, we need to add 았/었다 to the stem of a word (or 였다 in the case of 하다). Following the rule above, 았다 is added to words with the last vowel being ㅏ or ㅗ and 었다 is added to words with the last vowel being anything but ㅏ or ㅗ. Finally, 였다 is added to words with the last syllable being 하. For example:

나는 밥을 먹다 - I eat rice
The last vowel in the stem is ㅓ. This is not ㅏ or ㅗ. So, we add 었다 to the stem:
나는 밥을 먹었다 - I ate rice

나는 문을 닫다 - I close the door
The last vowel in the stem is ㅏ. So we add 았다 to the stem:
나는 문을 닫았다 - I closed the door

나는 한국어를 공부하다 - I study Korean
The last syllable in the stem is 하. Therefore, we add 였다 to the stem:
나는 한국어를 공부하였다 - I studied Korean

What makes this complicated (at first) is that for verbs that have a last syllable that end in a vowel (including 하다), the 았다/었다 gets merged to the actual stem itself. This is how 아 and 어 merge with syllables ending in a vowel:
• 아 + 아 = 아 (example: 가 + 았다 = 갔다)
• 오 + 아 = 와 (example: 오 + 았다 = 왔다)
• 우 + 어 = 워 (example: 배우 + 었다 = 배웠다)
• 이 + 어 = 여 (example: 끼 + 었다 = 꼈다)
• 어 + 어 = 어 (example: 나서 + 었다 = 나섰다)
• 여 + 어 = 여 (example: 켜다 + 었다 = 켰다)
• 하 + 여 = 해 (example: 공부하다 + 였다 = 공부했다)

Many people have asked me "how do I merge 아/어 to complex cowels like ㅠ, ㅑ, ㅔ, etc...?" You will find that the stem of almost all verbs and adjectives in Korean do not end in these complex vowels. The most common words I can think of that have stem that ends in one of these complex vowels are:

바래다 - to fade
매다 - to tie up
메다 - to put on/carry something on one's shoulder

With these words (and others like it), the same rule applies as above. That is, the final vowel does not end in ㅏ or ㅗ, so we need to add 어 plus whatever we are adding. With these complex vowels, it is irrelevant if you merge the addition to the stem. Both forms (merged and non-merged) would be correct.

For example:
바래 + 었다 = 바랬다 or 바래었다
매다 + 었다 = 맸다 or 매었다
메다 + 었다 = 멨다 or 메었다

Here is a more detailed breakdown:
오다 - to come
The last vowel in the stem ends in a vowel, 았다 can merge with 오:
삼촌은 가게에 왔다 - (My) uncle came to the store

던지다 - to throw
The last vowel in the stem is ㅣ. So we add 었다 to the stem.
나는 공을 던지었다 - I threw a ball
But, because the stem ends in a vowel, 었다 can merge with 지:
나는 공을 던졌다 - I threw a ball

공부하다 - to study
The last vowel in the stem is 하. So, we add 였다 to the stem.
나는 한국어를 공부하였다
But, 하 and 여 can be merged to formed 해:
나는 한국어를 공부했다 - I studied Korean

Future Tense

Future tense is easy, and is simply a matter of adding 겠다 to the stem of a word. Unlike the past and present tense conjugations, there is no difference if the stem ends in a vowel or a consonant. For example:
나는 먹다 - I eat
나는 먹겠다 - I will eat

나는 가다 - I go
나는 가겠다 - I will go

나는 배우다 - I learn
나는 배우겠다 - I will learn

Two verbs specifically that are often conjugated in the future tense without actually having a meaning in the future tenses are 알다 (to know) and 모르다 (to not know). I don't want to make any example sentences (because they would be too complicated at this point), but it would be good to remember that the words 알다 and 모르다 are often conjugated to 알겠다 and 모르겠다. Although they are conjugated to the future tense, those two words are typically used to express that somebody knows/don't know something in the present tense.

Check out the table giving a breakdown of verbs in the past, present and future forms: