Mr. Bailey said he might take that approach, investing a set sum every month, so that he felt better if the market went into a protracted decline. “It might feel like I’m getting some bargains that way,” he said.

Are these prices really bargains?

Brian deWit of Memphis said he had been through major market declines before and viewed them as opportunities.

In a note, he wrote: “Don’t you just love a sale!?”

We chatted about whether stocks were really on sale. Yes, prices are much cheaper compared with several months ago. In that sense they are bargains, I said. But based on standard long-term metrics — comparisons of share prices to corporate earnings or to the value of the assets owned by companies — stocks still aren’t all that cheap.

More important as an investor is what stocks will be worth in one year, or three years or five or 20 or more. Since we don’t know the answer, the issue, really, is how long you can afford to wait. Mr. deWit said he had time — and, if need be, would pass his assets on to his daughter. “Eventually, the market will come back,” he said.

Lacey Volk of Pittsburgh had a similar question. She puts money into index funds regularly. “I’ve continued to invest the same amount during this downturn, and I just check my balance less frequently,” she wrote. “I’m in it for the long term so not too worried. Is it accurate to think ‘stocks are on sale right now’?”

In our conversation, she explained that she graduated from college in 2006 and that during the devastating bear market that began in October 2007, she lost much of the money that her parents had put away for her in a mutual fund. The U.S. stock market didn’t fully recover its losses until March 2012, according to a comprehensive database developed at the University of Chicago, known as CRSP (pronounced “crisp”), for the Center for Research in Security Prices.

Ms. Volk said she had sold her holdings at a loss before the market turned around, and “didn’t fully understand what was going on back then.” That experience led her to adopt a buy-and-hold approach, she said, but she wondered whether she could rely on it.