은/는 and 이/가 are probably the most confusing Korean particles (case markers) for Korean language learners.
Even the professors of Korean language find it very difficult to explain the exact difference between these two particles and the way they are used. We will try to simplify things a bit here so that it’s easy for you to understand the difference.
은/는 are called Topic particles while 이/가 are called – Subject Particles. The confusing thing is that topic and subject are sometimes not clearly distinguishable. The person of thing that is the main focus of the sentence is called the topic. The subject of the sentence is not always the topic.
For example, in the sentence “오늘은 날씨가 좋아요.” subject of the sentence is 날씨 (Weather) while the topic of the sentence is 오늘 (Today).
The subject of a sentence can also be the topic of the sentence and vice versa.
In fact, in most of the situations 은/는 and 이/가 are interchangeable. ‘이것은 책입니다’ and ‘이것이 책입니다’ are pretty much the same thing.
There are some situations when you are supposed to use any one of these particles but even if you use the wrong one, it’s not that the sentence becomes incomprehensible or something. People will still understand what you want to say. So you don’t need to take too much stress.
Just remember some rule of thumbs about the usage of 은/는 and 이/가 and you will be fine.
- When it’s a negative sentence with verb ‘to be’ (아닙니다 or 아니에요 i.e. is/am/are + not), you always have to use 이/가 with the preceding noun. Ex: 이것은 책이 아니에요.
- If you are using 있다/없다 you should always use 이/가 with the noun before it. Ex: i) 펜이 있어요? ii) 저는 내일 시간이 없어요.
- Generally when there are two nouns in a sentence and a descriptive verb (or adjective) has been used, use 은/는 with the first noun and 이/가 with the second. Ex: 오늘은 날씨가 좋아요. 이 식당은 음식이 맛있어요.
- When you want to show contrast or emphasise a noun, you should use 은/는. For example – 품질이 좋은데 가격은 너무 비싸요. (Quality is good but the price is too expensive.)
Note that we have simplified the rules. There are more complicated rules and explanations but we don’t want to confuse you more. If you follow the rules mentioned above, you should be fine in most of the stituations.