In 1978, Donald Gunn was a creative director for the advertising agency Leo Burnett. Though his position implied expertise, Gunn felt he was often just throwing darts?relying on inspiration and luck (instead of proven formulas) to make great ads. So, he decided to inject some analytical rigor into the process: He took a yearlong sabbatical, studied the best TV ads he could find, and looked for elemental patterns.

After much research, Gunn determined that nearly all good ads fall into one of 12 categories - or "master formats," in his words.

Slate's slide show presents some recent ads exemplifying each of Gunn's 12 basic categories.

View the slide show at Slate