It’s not enough to say that markets could freeze up, loans could become impossible to get and the economy could slide into its worst downturn since the Great Depression. For now, the crisis has had little effect on most Americans, beyond their 401(k) statements. So to them, the specter of a depression can sound alarmist, and the $700 billion bill that Congress voted down this week can seem like a bailout for rich scoundrels.

Mr. Bernanke and his fellow worriers need to connect the dots. They need to use their bully pulpits to teach a little lesson on the economics of a credit crisis — how A can lead to B, B to C and C to Depression.

Let’s give it a shot, then.

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Why are we talking about the Depression, anyway?

Almost no economist thinks that even a terrible downturn would look like the Depression. The government has already responded more aggressively than it did in Herbert Hoover’s day. So a Depression-like contraction — a 30 percent drop in economic activity — is highly unlikely. The country is also far richer today, which means that a much smaller portion of the population is living on the edge of despair. No matter what happens, you’re not likely to see shantytowns.

But the Depression is still relevant, because the basic mechanics of how the economy might fall into a severe recession look quite similar to those that caused the Depression. In both cases, a credit crisis is at the center of the story.

At the start of the 1930s, despite everything that had happened on Wall Street, the American economy had not yet collapsed. Consumer spending and business investment were down, but not horribly so.