Already hearing holiday and Christmas songs everywhere? No doubt Mariah Carey's "All I Want for Christmas is You" is heard in a lot of malls, stores and establishments. It is considered to be one of the Christmas songs in the past two decades that has reached a height of popularity.

According to Adam Ragusea, a journalism professor at Mercer University, Mariah Carey's song is a classic because of the chords, as reported by Vox.

Ragusea said there are 13 distinct chords that makes Mariah Carey's "All I Want for Christmas is You" so special, as reported by Slate. He explains that the chords create a melody that is considered quite Christmassy.

Mariah Carey's song is not only a holiday classic but it is also a holiday staple. And it is because of a certain Christmassy chord that Ragusea believes is the reason why it works. He points out that the a minor subdominant, or "iv," chord with an added 6 when singing "underneath the Christmas tree" is just one of the many distinct chords that make it work. The professor also found the same chord in Irving Berlin's "White Christmas."

"All I Want for Christmas is You" was lauded and highly praised in the charts. It was also considered to be one of the few worthy modern additions to the holiday canon. Even Rolling Stones described it as a holiday standard. The song went Christmassy-viral everywhere. The song itself has earned a spot in holiday phone ring tones and sold millions of digital downloads.

And although the song was released over two decades ago, many still find the harmony, rhythm, instrumentation and lyrics of the song very well connected to both Christmas and R&B music.

Now, the song is making its way up the holiday Billboard charts. And Professor Ragusea believes Mariah Carey's song is going to last forever.

Check out Mariah Carey's performance below: