I ' ve heard I IV II V before a few timesBlue Oyster Cult Black BladeFl 7 bM ? t 13 sPuddle of Mudd She Hates MeVbgT 70 vuyAQAnyway , this is a secondary dominant . This is when we ' re using the chord as a dominant of the next chord , as if it were a minikey change . So in the key of C , C F D GThe D would be the dominant of G , and sets it up nicely because the VI relationship is the most strong in Western music . The D doesn ' t fall into the key of C , and if you were soloing , you would use the F # instead of the F . Another example of a secondary dominant is Sublime Santeria where the chords go E G # C # m B . That would be a I III vi V , where the III would normally be a iii , but in thie case it ' s a secondary dominant of the C # m . You can read more about secondary dominants here