David Foster and Katharine McPhee don't abide by rules in their marriage.

In an interview with People magazine, Foster, 74, explained that being flexible with McPhee, 39, works best for their family.

"[Marriage] is a moving target, as you probably know," the music producer told the outlet. "If you’re a parent, then you absolutely know."

When asked if there are any rules in their marriage, Foster said there aren't "any hard and fast rules."

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Foster and McPhee tied the knot in 2019. They are parents of a 3-year-old son, Rennie.

Rennie is the sixth child for Foster and the first for McPhee. The record producer, who was previously married four times, is also a father to daughters Alison, Amy, Sara, Erin and Jordan.

"Sometimes, parents can agree to disagree and then agree on most things and a different philosophy on other things," he said. "But it just works itself out."

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David has been open about how he and Katharine have a different approach to parenting, including how they discipline. But he noted that their arguments and disagreements are "all for the betterment of the child. Both of us, that’s what we work towards." 

In November, Foster told the outlet, "I want to start disciplining [Rennie], and Kat's not really down with that."

"No, that's not true," McPhee responded at the time. "I just want to discipline in my own way. There's the more old-fashioned way of disciplining, which involves timeouts and things like that. My take is that you can have more mindful parenting as opposed to just assuming that a 2- or 3-year-old can have time alone to reflect on what they've done poorly."

McPhee and Foster also work together professionally. The two recently collaborated on a seven-track holiday album titled "Christmas Songs."

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"I produced our Christmas album, but it wasn’t like producing," Foster said. "It was just me and my wife in the studio just hanging out, making music. My wife and I have this great relationship, and it’s always fun to make music with her. She’s an incredible singer and can do anything I ask, which is fantastic in the studio."

David acknowledged that his wife has taken a break from her solo music career, but fans can expect new material from her "very, very soon."

"She’s a great mom and obviously a great singer, performer and actor, but COVID sort of stopped everybody in their tracks for quite a while," Foster explained. "It coincided with her becoming a new mom, and she loves being on the road with me, but she’s ready to get back to the life she had before me as well as that." 

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In November, McPhee opened up to People about when she argues the most with Foster, which is almost always while driving.

"That's less of a pleasure. He's always like, 'Where do I turn now, where do I turn now?" she told the outlet, laughing. "The only time we get into arguments is when I'm helping him navigate freaking directions."

Foster added, "It's true. Because she's a backseat driver!" McPhee replied, "I'm not. I just know how to follow directions."