In response to the infringement claim, Ilene Farkas, Sheeran's attorney, argued that any elements of Thinking Out Loud" bearing a resemblance to Let's Get It On were not subject to copyright protection because those elements are basic "building blocks" of music regularly used by artists everywhere.
As such, she argued that they were not subject to protections against infringement under relevant US law.
In response, Keisha Rice, representing the heirs of Ed Townsend, contended her clients had not claimed to own the basic musical elements but rather "the way in which these common elements were uniquely combined" and presented a video which described as a "smoking gun" showing Mr Sheeran move seamlessly between Thinking Out Loud and Let's Get It On at a live show.
Mr Sheeran responded by testifying that he frequently performs such medleys in concerts which are made possible by the limited harmonic palette of mainstream pop music.
At one point, Mr Sheeran even broke out his guitar to rebut testimony provided by an expert musicologist acting for the heirs of Ed Townsend.
In closing arguments, Mr Sheeran's attorney said that her client had created Thinking Out Loud independently and attacked the plaintiffs' case as one "that should have never been brought".
Ms Farkas also told the jury that if the plaintiffs succeed, it could have a devastating impact on future musicians because it would remove "an essential element of every songwriter's tool kit and creativity would be stifled for fear of being sued".