We walked down to the Plaza yesterday in 90 degree heat, and enjoyed lunch at Zoe’s. On the way back, we skipped the serious hill and instead strolled around the other way, passing the Kemper Museum.

I persuaded #2 daughter and her beau to go inside. I made a $10.00 donation for us and bought several books to take home for the children.

I have to admit that this is a larger donation than I normally would have made. I think I usually would have dropped $5.00 in the donations box, especially since we saw just two rooms of ehibits.

But we had been talking about the Free Rider phenomenon. When there is a public good — we were talking about Little Libraries as an example, but the Kemper is another — which can be accessed with little or no investment, there will be people who make a donation or pay their taxes or what have you, and there will also be people who use the service without paying. Those are the Free Riders.

The Free Rider problem arises when too many Free Riders take advantage of the goodies, compared with the number of people investing in those goodies. At some point, it is no longer possible to pay for those goods.

The Little Library allows people to take books without putting any in. But a classic example of the Free Rider problem is the environment. It’s not possible to restrict the benefits of environmental responsibility to those who make an effort toward sustainability. Free Riders benefit just as much as the environmentally responsible.

Mr. Trump has pulled out of the Paris Accord, making the United States (potentially) a Free Rider. We are now in the same group as Nicaragua and Syria and — oh, yeah, no other nation in the world.

This is an embarrassment for us and a potential problem.

And I suppose the reminder of the Free Rider problem caused me to increase my donation.