Premise and plot. They're both essential to every story, but they're not the same thing. I've had books where I loved the premise, but didn't love the plot. I saw a TV commercial for the movie Ted that showed the premise, but not the plot, and started thinking about the difference.
This is the basic idea. For example, the premise of Harry Potter is a boy attending a school that teaches wizardry. The premise of Twilight is a girl meeting a family of vampires. It's the foundation that the plot of which book and the overarcing plot of the series is based on.
This is the arc that drives the story. It's the escalating conflict and has an obvious beginning, middle, and end. Going back to the Harry Potter example, this would be Harry's fight against Voldemort across the series. In the Twilight example, the plot would be the girl falling in love with the vampire and wanting to become one herself.
Here's the commercial for Ted that brought about this whole thought process. It showed the premise -- a boy makes a wish and his teddy bear comes to life, but boy grows up -- but little of the plot. Does the man have to figure out how to turn the teddy bear back into a stuffed animal? Does the man go on a hunt to find a child for the teddy bear to live with? Is the teddy bear kidnapped by evil scientists intent on figuring out how it came to life?
Now, which is more important: plot or premise? Think of the premise as the foundation and the plot as the actual house. If the foundation isn't stable, the whole house will come tumbling down. However, if the roof has holes in it, or the paint on the walls is peeling, or the basement is flooded, no one's going to want to live in the house no matter how stable the foundation is. The same goes for novels. You can have the best premise in the world, but if the plot isn't well-executed then the story still isn't going to work out.
What do you think? Are premise and plot two separate things? Which one is more important? Would you read a book with a great premise without a sense of the plot?