Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
First-Person
Yeah, Thomas Paine might act like he knows everything about everything sometimes, but he's still just a limited First-Person narrator in this book. He even refers to himself as "the author" instead of "I," but no amount of fancy linguistic trickery is going to throw us off the scent of a First-Person narrator here.
It's interesting to see just how much Paine tries to sound like a third-person objective narrator when he writes stuff like, "In the following sheets, the author studiously avoided every thing which is personal among ourselves" (I.3). Nice try, Tommy. We see you hiding there.
In other words, he's trying to tell us that his common sense has made him into an objective source of knowledge on American independence. It's all just a trick to make his arguments more credible in our minds, but you have to admit it's an effective one. We sometimes forget that he's just one man giving his first-person opinion, and think of him as The Voice of Reason, er, Common Sense.