swear someone to something
to cause someone to take an oath pledging something, such as silence or secrecy, about something. I swore Larry to secrecy, but he told anyway. We were sworn to silence about the new product.
swear something to someone
to pledge or promise something to someone. I had to swear my allegiance to the general before I could become one of his bodyguards. We swore our loyalty to our country.
swear to something
to claim that what one says is absolutely true. It is true. I swear to it. I think I have remembered it all, but I couldn't swear to it.