Ed Sheeran Defends His 'Thinking Out Loud' in 'Let's Get It On' Lawsuit

Ed Sheeran not only thinks the claim he ripped off a Marvin Gaye classic is total rubbish, but one of the people suing him doesn't even have a leg to stand on ... according to new docs.

We broke the story ... Sheeran was sued nearly 2 years ago for allegedly jacking the heart of Gaye's sexy song, "Let's Get It On," for his hit track, "Thinking Out Loud," and after some legal back-and-forth, Ed's finally fighting back.

Sheeran claims the alleged similarities between the 2 jams are simply because the chord progressions and drum patterns are "extremely commonplace" in the music world. What's more -- according to the docs -- is that the similar elements of 'LGIO' are unprotectable, public domain elements.

He also claims there are little to no similarities when it comes to the vocals and song structures.

The kicker though -- Sheeran claims the woman suing him on behalf of the late Ed Townsend, who co-wrote the tune with Gaye, has no right to do so because, while she might be Townsend's biological daughter ... she was adopted by others at birth.

Sheeran claims this means under California law, she has no standing in the case.