If your father is a judge, he is included in "Elohim you shall not curse." And if he is a Nassi ("president"), he is included in (Ibid.) "and a Nassi in your people you shall not curse." If he is neither, it follows by induction from both, viz.: A judge is not like a Nassi, and a Nassi is not like a judge. The common element between them is that they are "in your people," and you are exhorted against cursing them. Your father, too, is "in your people," and you are exhorted against cursing him.