You exist because others percieve your existence , you are a social being that exists because he can be seen heard touched etc. by other people ,if you were alone , and no one else existed you could not prove that you exist , if you can use one of your senses to comprehend the existence of something that means the object/person is real (and don't give me the air example , air exists but we can't see smell touch taste or hear it , it's existence is sustained by the fact that we are alive , and it can be chemically analized ) , you can't aknowledge the existence of something that is not real and palpable , scientifically speaking of course , no "God" flaming please .