The Top Three Economic Concepts

A writer asked Greg Mankiw if he could teach every American teacher three economic concepts, what would they be?  Here was his reply:

I organized my principles text to put the most important concepts toward the front of the book. If I had limited time to teach a basic course, I would try to get through the first 10 chapters (out of 36 in the book), perhaps skipping chapter 2 on methodology and 5 on elasticity. Summarizing these chapters in three big ideas is hard, but here goes:

1. Comparative advantage and the gains from trade.
2. Supply, demand, and the efficiency of market equilibrium.
3. Market failure, such as externalities, and the role for government.

The lesson is that we can all gain from economic interdependence and that markets are a good, but not always perfect, way to coordinate people in an interdependent world.

Not a bad list.  I would add a nuance to number 2 with emphasis on the emergent (undirected) process that determines prices in the marketplace, the role these prices have in conveying information, and how it helps coordinate the activity of individuals acting with limited, local knowledge.