It is not unusual for senior government officials to join the speaking circuit or take lucrative jobs in the private sector after leaving public office.
Mr. Greenspan was hired to consult for the hedge fund Paulson & Company, Deutsche Bank, and the bond investment firm Pacific Investment Management Company after stepping down as Fed chairman. After leaving the top job at Treasury, Timothy F. Geithner joined the private equity firm Warburg Pincus.
And Mr. Bernanke is free to speak about his views on the economy as long as he does not breach any confidentiality agreement.
"If they are saying something that they were saying as a public official, is there something wrong with that?" Mr. Greenspan said.
Since his busy week jetting around the world in March, Mr. Bernanke has made several other appearances, including at a private equity conference hosted by the Blackstone Group a few weeks ago. He is scheduled to speak in Pennsylvania at the Lancaster Chamber of Commerce's annual event on May 28, where members will pay $225 for a ticket.
Then things will pick up again for the former Fed chairman in the fall, when he is scheduled to speak at the SALT hedge fund conference in Singapore. Morgan Stanley is in discussions with Mr. Bernanke to have him also speak at a dinner on the sidelines of the conference.
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In November, over the span of two weeks, he is to give keynote speeches at a series of events in the United States, hosted by the Association for Financial Professionals; the Schwab Impact conference; and the Commercial Finance Association.
Though Mr. Bernanke has been busy traveling these days, he spends most of his time as an economic studies fellow at the Brookings Institution and is working on a book about his time at the Fed.
He also delivers pro bono speeches and does not always pocket all the fees, a spokeswoman for Mr. Bernanke at the Brookings Institution said. "In addition, he is donating hundreds of thousands to charity," she added.
The Washington Speakers Bureau, which coordinates Mr. Bernanke's speaking engagements, did not return calls.
Not everyone agrees with the fees that Mr. Bernanke charges.
"You can spend $250,000 for Bernanke's time at a private dinner, or you could just sit down and read what people like Janet Yellen and Mark Carney have to say," Mr. Rosenberg said, referring to the governor of the Bank of England. "You can actually do that for free and pretty much draw the same conclusions."