The Seventh Commandment says, “Thou shall not steal” but what does that mean? While the Catechism of the Catholic Church does admit of extraordinary circumstances where it can be moral to take another’s property (e.g., it’s not wrong to take an apple from someone’s orchard in order to feed someone who is starving), the essence of the seventh commandment is this: “It’s wrong to make something yours if it belongs to someone else.”

This goes far beyond the classic example of walking into a bank and saying “Stick 'em up!” Paragraph 2409 of the Catechism references the following sins against the seventh commandment:

• Stealing from employees by paying them less than what they’re work is worth.
• Stealing from employers by making...

Determining a bad idea’s antecedents usually is messy and often is impossible. Just when did a particular bad idea begin? Seldom is there an analogue to Athena coming fully formed from the forehead of Zeus.

Usually one bad idea derives from an earlier bad idea, which in turn derives from still earlier bad ideas. In order not to get lost in a long series that disappears into the mists of pre-history, you need to choose a point at which you can say, “For purposes of discussion, I count this as the origin of this bad idea.”

I’m going to blame last week’s same-sex marriage decision on the poet John Milton. Let me explain.

I don’t at all mean that Milton or any of his contemporaries or anyone for centuries following endorsed or even thought of same-sex marriage...