What is a patent really?

It's a contract with the public. You make your invention known and, for awhile, you will be granted a monopoly on its use.

Is that all we buy and sell are ideas?

Seems to me that products are the embodiment or manifestation of ideas. I think we have to buy the idea first. The product that goes home with us is then, maybe, a souvenir of our buying the idea. So powerful ideas.