The pair, alongside rapper T.I., have been battling Gaye's family since last year (13) over claims they revamped the soul singer's track Got to Give it Up without permission.
Thicke and Williams both recorded depositions regarding the matter in April (14) and they have now submitted new court documents to prove key differences between the songs.
In the documents, obtained by Tmz.com, the duo admits the repeated notes which open the song are very similar to Gaye's tune but then cite late composer Ludwig van Beethoven, claiming he also used the same device in a symphony. They use the example to prove musicians have been using the sequence for years.
Thicke hit headlines earlier this month (Sep14) when his deposition went public, revealing he took too much credit for the song and was "high on Vicodin and alcohol" when he recorded it.