In this lesson, we are looking at the sentence ending -(는)구나 and -(는)군요. -(는)구나 is used in 반말 (casual, informal language) and -(는)군요 is only used in 존댓말 (polite, formal language). When are they used?You use -(는)구나 and -(는)군요 when you just realized or found out about something for the first time, mainly to express your realization. You can sometimes use them to show that you are surprised, but this depends on the intonation of your sentence. Let's compare some sentences using the -(는)구나 or -(는)군요 ending with some plain sentences.1. 여기 있었어요. [yeo-gi i-sseo-sseo-yo.] = It was here.(존댓말) 여기 있었군요. [yeo-gi i-sseot-gun-yo.] = (I see that) it was here.(반말) 여기 있었구나. [yeo-gi i-sseot-gu-na.] (same meaning as above)2.  생각보다 비싸요. [saeng-gak-bo-da bi-ssa-yo.] = It's more expensive than I thought.(존댓말) 생각보다 비싸군요. [saeng-gak-bo-da bi-ssa-gun-yo.] = (I see that) it is more expensive than I thought.(반말) 생각보다 비싸구나. [saeng-gak-bo-da bi-ssa-gu-na.] (save meaning as above)3. 여기 살아요. [yeo-gi sa-ra-yo.] = I live here. She lives here. They live here. etc.(존댓말) 여기 사는군요. [yeo-gi sa-neun-gun-yo.] = (I see that) you live here. (반말) 여기 사는구나. [yeo-gi sa-neun-gu-na.] = (same meaning as above)Construction[Past Tense] Verb stem + -았/었/였군요 Verb stem + -았/었/였구나[Present Tense]- Action Verbs: Verb stem + -는군요/는구나 - Descriptive Verbs: Verb stem + -군요/구나-(는)군요 and -(는)군Generally, when you drop the -요 at the end of a Korean sentence, it becomes a 반말 sentence and it is the same with -(는)군요. Therefore, instead of saying -(는)군요, if you say -(는)군, it becomes the same level as -(는)구나. Even though the basic meaning is the same, however, -(는)구나 is more commonly used in spoken language and among females than -(는)군. Sometimes people would say -(는)군, but saying this will make your sentence sound a bit like written language and more masculin. Ex)이거 맛있구나. [i-geo ma-sit-gu-na]= (I didn't know before but I just realized that) this is delicious!이거 맛있군.[i-geo ma-sit-gun.]--> This sentence has the same basic meaning as the one above, but it sounds a litte more masculin and like written language. Nouns + -군요/구나 When you want to say "Noun + -이다", if the noun ends with a consonant, you keep the -이 and add -군요 or -구나. Ex)학생이군요. / 학생이구나. But if the noun ends with a vowel, you drop the -이 and just add -군요 or -구나. Ex)이거군요. / 이거구나. More Sample Sentences1. 여기 진짜 넓구나! [yeo-gi jin-jja neolp-gu-na!]= This place is so big!2. 이게 그거였군요! [i-ge geu-geo-yeot-gun-yo!]= So this was what you were talking about!3. 이렇게 하는 거군요.[i-reo-ke ha-neun geo-yeot-gun-yo.]= So this is how you do it!4. 벌써 11월이구나![beol-sseo si-bi-rweol-i-gu-na!]= (I didn't realize before but) it's already November!5. 어제도 만났군요. [eo-je-do man-nat-gun-yo.]= (I didn't know before but I just found out that) you met yesterday too.