Ed Sheeran is having a tough summer. In June, the writers of Matt Cardle’s single “Amazing” slapped Sheeran with a $20 million copyright infringement lawsuit, claiming that Sheeran’s 2014 song “Photograph,” from his album X, copied “note-for-note” Cardle’s “Amazing,” written in 2009. On August 10, Sheeran was hit with another copyright infringement lawsuit, this time by the heirs of Ed Townsend, who composed and co-wrote the lyrics for Marvin Gaye’s classic song “Let’s Get It On” in 1973. The latest lawsuit claims that Sheeran’s song “Thinking Out Loud” (Sheeran’s first Number One single, also from from X) possesses melodic, harmonic, and rhythmic elements that are “substantially and/or strikingly similar” to “Let’s Get It On.” It’s anyone’s guess as to how these lawsuits are settled, but an unfavorable verdict against Sheeran could have ramifications on songwriters everywhere.

In both cases, Sheeran is being sued because, in essence, the musical structure of his songs is too similar to someone else’s. For instance, the “Photograph” lawsuit alleges “The chorus sections of Amazing and the infringing Photograph share 39 identical notes – meaning the notes are identical in pitch, rhythmic duration, and placement in the measure.”

These types of cases, which come down to musical, as opposed to lyrical, similarities, seem to be up for grabs. In 2015, attorney Richard Busch, who is representing the writers of Matt Cardle’s “Amazing,” successfully sued Robin Thicke and Pharrell Williams in a copyright infringement case that claimed Thicke’s and Williams’s song “Blurred Lines” was too similar in musical structure to Marvin Gaye’s “Got to Give It Up.” A judge awarded Marvin Gaye’s family $5.3 million and a share of future royalties. On the other hand, in June, Led Zeppelin successfully defended itself in a copyright infringement lawsuit that claimed the opening chords to Zeppelin’s “Stairway to Heaven” plagiarized guitar chords in Spirit’s song “Taurus.”

Why did Led Zeppelin emerge victorious over musical infringement but Robin Thicke and Pharrell Williams did not? The answer will determine whether Sheeran is liable for millions of dollars in damages. And, as I blogged recently, the matter is a murky one. These factors will likely decide the outcome:

• How integral is the music to the entire song? This issue will likely determine whether Sheeran wins or loses. Thicke and Williams were successfully sued because the recurring backbeat and chorus that form the structure of “Blurred Lines” was too similar to that of “Got to Give It Up.” On the other hand, although the opening chord progression of “Stairway to Heaven” is similar to a guitar part in “Taurus,” the resemblance lasts but a few seconds. Thicke and Williams might have emerged victorious had a jury believed the same was true with “Blurred Lines” and “Got to Give It Up.” In Sheeran’s case, the lawsuits are basically arguing that Sheeran stole the foundation upon which he built his songs, as opposed to nicking just a few elements here and there. Based on the outcome of the “Blurred Lines” lawsuit, Sheeran is definitely in a tough position with both his lawsuits. He may very well need pay up.

• How original is the music in question? Team Led Zeppelin argued that the songs “Taurus” and “Stairway to Heaven” were based on common chord progressions that date back to the 17th Century and can be heard in songs such as the Beatles’ “Michelle.” In other words, the musicians were adapting music that is in the public domain, and any similarity to other songs was entirely coincidental. On the other hand, in the 1970s, George Harrison was successfully sued for copyright infringement because his song “My Sweet Lord” was too similar to a very distinctive, original melody in the Chiffons song “He’s So Fine.” Team Sheeran may find themselves needing to prove that the songs in question are not entirely original — an argument that comes down to successful homework and producing musicologists who sound convincing enough. But this point can be difficult for a defendant to successfully argue. With “Taurus” and “Stairway to Heaven,” a jury determined that despite Team Led Zeppelin’s arguments, “Taurus” was original enough to justify Spirit owning its copyright.

In any event, songwriters have been put on notice: attorneys are watching your every move. What you determine to be creative inspiration could land you in court. And you might not possess Led Zeppelin’s deep pockets to defend yourself. The band paid $800,000 in legal fees in the “Stairway” case. Your creative reputation could come down a judge, a jury with zero musical knowledge, and a whole lot of money.