I’m confused. Aren’t all our votes for sale? Each candidate tries to bribe us with future benefits of all sorts. Basically, a campaign is an effort to buy votes wholesale.

Why do you think Barack Obama is “refining” his positions on so many issues? He’s in the process of buying the independent votes he needs to win in November. This creates a problem. If he goes too far in buying independent votes, he may have to return votes he already bought from left-leaning Democrats during the primaries. His updated positions on the Iraqi occupation, the death penalty, handgun bans, campaign finance, money for religious groups, and immunity for telecom companies that illegally helped the Bush administration wiretap us without warrants have upset people who thought their vote sales were final. In politics no sales are final.

John McCain may have a bigger problem. He’s had trouble buying votes from the conservative base of the Republican Party. Those voters don’t seem eager to sell their votes to him because they don’t like what he’s promising to pay in return. While McCain is trying to close the deal with conservatives, he also needs to buy votes from independents. That’s one of the dilemmas of politics. If you buy votes from, say, fiscal conservatives, you might have a hard time also buying votes from advocates of climate control through cap and trade, which would be a tax on energy production.

Keeping most campaign promises costs money. For politicians, money comes from the taxpayers, who are forced to surrender their cash whether they like it or not. As H.L. Mencken understood, “Every election is a sort of advance auction sale of stolen goods.” So the only difference I see between a politician who buys a vote and an eBay bidder who buys it is that the bidder spends his own money. Since people spend their own money more wisely than they spend other people’s, we can conclude that the eBay sale might be preferable.

I’m sure many people were appalled that young Mr. Sanders — eligible to vote in his first presidential election — would even dream of selling his vote. How cynical he is, they must be thinking.

I don’t think he’s cynical. I think he’s naïve.

He thought someone would be willing to buy his vote for $10 or more. Why would anyone do that? One vote isn’t going to change the outcome of the election. The chance that McCain and Obama will tie in any of the 50 state elections is roughly zero. No single vote will be decisive. So we can be certain that for any voter, on election day it won’t matter if he stays in bed.

Now, if a person’s one vote doesn’t matter, are two votes — his own and the vote he buys — likely to change the outcome of the election? Of course not. Yes, his vote total would increase 100 percent, but that only shows you how misleading percentages can be. It’s still only one more. So why would anyone pay $10 for it? If there is such a person, tell him I have newborn unicorns for sale.

Mr. Sanders’s entrepreneurship would have run into other problems. How would the buyer know the vote he purchased was cast for his favorite candidate? There’d be no way to prove it. He’d have to rely on Mr. Sanders’s honesty. That strikes me as a big risk to take with a stranger.

But I guess it’s no bigger than the risk you take when you trust the honesty of a politician when you sell him your vote.