I bet it is. * The subject markers 가/이 are used to give emphasis to the subject. 제가 그사람 봤어요 * The topic marker 는/은 is normally used in a subject that is going to be the topic of the sentence, or that has already been mentioned, and that could easily be omited. 김 선생은 너무 너무 좋아해요. Mr Kim is extremely nice. (Talking about Mr. Kim, guess what?, he is extremely nice) 이개가 내 개에요. (그는) 착해요. This is my dog. (He) is nice. It has other uses though. For example, you can use it to mark a contrast between two things (one of which can be implied rather than stated). 그선생님이 프랑스말을 선생이세요? Is he the teacher of French? 아니에요. 한국말은 선생이세요 . No, (he) is the teacher of KOREAN And it can be used in the subject or in the complement, sometimes several times in the same sentence.

Your question is similar to Yume's question. prob you don't distinguish those usage between 가/이 and 는/은. I will link for ya. http://www.italki.com/Answers/question/57356.htm hope it can be helpful. have a great evening. :)