Republican presidential candidate and former neurosurgeon Ben Carson warned that if the definition of marriage were changed to include gay couples, it would also have to be changed to incorporate other types of unions.

But Carson, in an interview with CBNC’s John Harwood, wouldn’t elaborate on what other “groups” would be allowed to marry.

Carson started out saying if you “change the definition of marriage for one group, what do you say to the next group?”

“What is the next group?” Harwood interjected.

“Do you say, ‘well we changed it for this group but that’s it, we’re not changing it for anybody else?” Carson asked. “Does that seem fair?”

“Well, but what other groups are there?” Harwood asked.

“There are more groups, I guarantee,” Carson said. “I think you know there are more groups. Everybody knows there are more groups.”

“Honest to God, I don’t know what you’re talking about,” Harwood said.

“Other variations on traditional marriage. You don’t think there’s any others?” Carson asked.

“You mean like bigamy or something?” Harwood asked.

“That’s a possibility, that’s a possibility,” Carson said. “Why would you stop with one group being able to change it and then say to the next group ‘you can’t change it’?”

Harwood said he wasn’t “advocating” one way or another there.

“I’m just asking a question,” Carson said.

As TPM previously noted, Carson said in an interview with Newsmax that if the Supreme Court were to rule in favor of same-sex marriage, the President of the United States still wouldn’t have carry out that ruling.

Watch the exchange below: