“Blurred Lines” are indeed imminent for Robin Thicke and the estate of Marvin Gaye — the two are now officially involved in a legal battle.

Some background: In August, Thicke, along with producer Pharrell Williams and rapper T.I., filed a pre-emptive copyright protection suit in federal court in California against both the family of Marvin Gaye and a publishing company. Thicke denies copying Gaye’s “Got To Give It Up” song for “Blurred Lines” — which still stands as this year’s biggest single, sitting atop the Billboard Hot 100 chart for 13 weeks and selling more than 6 million copies.

This past Wednesday, two of Marvin Gaye’s children countersued Thicke and his collaborators for copyright infringement. Nona Gaye and Frankie Christian Gaye accused Thicke, Pharrell, and T.I. of copying Gaye’s hit “Got to Give It Up.” The pair also alleged that music company EMI failed to protect their father’s legacy, and that Thicke also used Gaye’s song “After the Dance” in his song “Love After War.”

We asked Rose Massary, Esq., associate attorney for entertainment and sports law firm Romano Law, PLLC in New York City. for a professional opinion. Here’s her take:

“In copyright law, one of the things that they look for to see if there’s an infringement claim is substantial similarity and access to a copyrighted work,” said Massary. “So two things here may be proven. Marvin Gaye’s work has been public for quite some time; it’s considered classic and iconic.”

“Sometimes a new copyright work can be from using someone else as an inspiration, but the new work has to be transformed into something really different from the original. The Gaye family references two admissions by Thicke — that his intention in creating ‘Blurred Lines’ was to make something like Marvin Gaye’s “Got to Give it Up,” says Massary. “Based on the facts of the counterclaim, it is apparent that Mr. Thicke had access to Mr. Gaye’s work and used it as inspiration.”

According to the Hollywood Reporter, the Gayes cited Thicke admitting he received inspiration from Gaye to GQ, saying, “Pharrell and I were in the studio and I told him that one of my favorite songs of all time was Marvin Gaye’s “Got to Give It Up.” I was like, ‘Damn, we should make something like that, something with that groove.’ Then he started playing a little something and we literally wrote the song in about a half hour and recorded it.”

“In procedure, I’m not sure if it’s different in California since I’m a New York attorney, but if there’s questions of facts of exactly what happened and which side did what, it’s not for a judge to determine,” Massary continued. “If you copy something exactly, word for word, or if it’s the exact same video or song it’s easy to prove, but if it’s not exactly the same, it’s all based on what an objective reasonable person would determine. At the end of the day it’s just a question of what would the fact-finder or the jury decide whether Mr. Thicke merely blurred the line, or actually crossed it.”