Subject Particle - 이/가

이 and 가 are subject particles. Particles which come after a noun and shows "subject" are: -께서, (에)께서, etc.

When the noun ends in a consonant, you will use "이".

When the noun ends in a vowel, you will use "가".

Here are two examples:-

1. 연필 : 연필 + 이 ---> 연필이
2. 딸기 : 딸기 + 가 ---> 딸기가

When "이" and "가" is attached at the end of "나, 너, 저, and 누구," the words change into:

1. 나 ---> 내가
2. 너 ---> 네가
3. 저 ---> 제가
4. 누구 ---> 누가

Here are some examples using the word change:-

1. 내가 가요
2. 네가 갔니?
3. 제가 가겠습니다
4. 누가 갑니까?

I'll now give you some example sentences, including their English translation:-

1. 연필이 있습니다 --- There is a pencil.
2. 안경이 없습니다 --- There is not a pair of glasses.
3. 시계가 비쌉니다 --- The watch is expensive.
4. 딸기가 맛있습니다 --- The strawberry is delicious.