Let's learn about "진심이야"

(나) 진심이야 : I mean it

[other expressions]

- (나) 진심이다. (to younger people or friends)

- (나) 진심이네. (to younger people or friends)

- (나) 진심이야. (to younger people or friends)

- (나) 진심인데. (to younger people or friends)

- (저) 진심이네요. (honourific by '-요')

- (저) 진심인데요. (honourific by '-요')

- (저) 진심이에요. (honourific by '-요')

- (저) 진심입니다. (formal; honourific by '-ㅂ')

[explanations]

* 나 : I (non-honourific word); 나 can be replaced by 난

* 저 : I (honourific word); 저 can be replaced by 전

* -는 : a particle makes 나 / 저 subjective after a word ends in a vowek

* 난 : a short form of 나는

* 전 : a short form of 저는

* 진심 : the whole [true] heart; sincerity

* -이다 : be

* 입니다 : 이(the stem of 이다) + -ㅂ니다(an honourific descriptive verb ending suffix by '-ㅂ')

* a verb + -이다 / -이네 / -이야 / -인데 : a non-honourific descriptive form of 이다

* a verb + -네 / -인데 + -요 : an honourific verb ending suffix

* a verb + -예요 / -이에요 / 입니다 : an honourific descriptive form of 이다 by '-ㅂ' / '-요'

* a noun ends in a consonant + -이에요

ex) 진심이에요

* a noun ends in a vowel + -예요

ex) 정말 아름다운 미소예요