When watching Star Wars: The Empire Strikes Back, I noticed that what is probably the movie's most famous quote wasn't said the way I expected it to be. When Darth Vader tells Luke the truth about his father, he says "No, *I* am your father", stressing the "I" in that sentence. This confuses me somewhat, as in my native language, emphasis would instead be placed on "am" due to the context of Luke's previous statement "He told me you killed him." So in my language, it would be "No, I *am* your father", emphasising the fact that Vader did not kill him, but that he was him. So in English, it is obviously different and the rule of stressing verbs that contradict a previous statement apparently does not exist...?
Therefore, my question is twofold: Is there a rule in English that explains why Darth Vader stresses "I" instead of "am" in this scene, and is there a definitive list of rules on which words to stress/emphasise in a sentence when speaking?