At a wedding a few years ago - the choruses are the same chord progression and almost the same melody.

And "Let's get it on" was for the honeymoon...

but the melodies don't.

There are a lot of songs with similar chord progressions - a lot of three chord rock & roll and blues for example.

I always thought the melody carried the day in musical copyright. Maybe this case is going to make some law ... in that I'm surprised it is proceeding based upon what I heard. I thought the case against Led Zeppelin was better yet agreed with the result.

Then there's a chance plagiarism is involved.

It's not just the chord progression and melody, it's also the rhythm, the starts and stops.

My band was able to blend the two songs seamlessly.

Compositions
The U.S. Copyright Office recognizes two types of copyright claims for melodies. The first is the copyright of a musical composition, which recognizes the songwriter for creating the song. Melodies may be copyrighted as compositions if they’re fixed as sheet music or a recording. Sound recordings are sounds made at the actual recording sessions when a musician records a song. While a songwriter who writes and records a melody -- such as a performing musician recording an album -- can claim copyright on the composition and recording at the same time, a musician who records a song that another person wrote may only register the copyright on her sound recording.

The air that I breathe with a slightly different melody, and Tom Petty sued Sam Smith for stealing one of his songs a few years ago- similar melody,same chords and rhythm.