2nd story: interprets, gives a point of view on, and/or adds controversy to the facts of the first story. By adding controversy, I mean it takes a position on the facts which is not obvious, a position which reasonable person could disagree with. A person reading a 2-story thesis thinks: "That's an interesting point of view; now prove it to me." By controversial, I do not mean this thesis has to be absurd or idiosyncratic; you'll never be able to convince your reader of that kind of argument. Rather, I mean it takes one position out of a number of positions.
3rd story: relates the 2-story thesis to the bigger picture, explains its significance, sets it a new context. This is the most difficult type of thesis to describe (and write) because it can take so many forms. I find it helpful to think of this story "opening out" - as if though a skylight - to a wider view. It is the answer you get when you ask of a 2-story thesis, "so what?" The reader should say: "I see why this argument matters." The pitfall in this type of thesis, that you want to be careful to avoid, is that it can get too ambitious, and try to make a bigger claim that you're able to substantiate (e.g. "My analysis of Sonnet 18 shows that all Western poetry is morally bankrupt and self-serving."
Examples
1st story: Anne Bradstreet's "The Author to Her Book" employs metrical substitution, imagery that depicts her writing as illegitimate child, and an allusion to Greek mythology.
2nd story: Anne Bradstreet's "The Author to Her Book" conveys her vexed relationship to her writing.
3rd story: Anne Bradstreet's "The Author to Her Book" reflects her vexed situation as an author, a relationship that largely reflects the prevailing attitudes about writing and gender in the New World.
As you can see, each story depends on the one below it. It is difficult, to say the least, to build a three-story house without a first story. The same holds true with a thesis: a two-story thesis needs a first story, and a three-story thesis needs a first and second story.
