FORMAL OUTLINE
Thesis statement (main idea)
I.	First main topic
A.	First subordinate idea
1.	First supporting idea
2.	Second supporting idea
3.	Third supporting idea
B.	Second subordinate idea
1.	First supporting idea
2.	Second supporting idea
II.	Second main topic
A.	First subordinate idea
1.	First supporting idea
2.	Second supporting idea
B.	Second subordinate idea
1.	First supporting idea
2.	Second supporting idea
a.	First supporting detail
b.	Second supporting detail

Each level contains at least two parts, so there is no A without a B, no 1 without a 2.