이 and 가 is something like IS. you know theres no postposition in english. im not sure im right because my korean teacher is not korean. but korean is perfect language. i learned likethis: in english: to eat apple, say to epple, apple said, apple is. you see, just change the order. but in korean: 사과를 먹다, 사과에게 말하다, 사과가 말했다, 사과는. not change order only form is change. sorry for my english but i did my best haha