chord) or similar transitional harmonies. "Often, a two-phrase verse containing basic chords is followed by a passage, often harmonically probing, that leads to the full chorus." Often, when verse and chorus use the same harmonic structure, the pre-chorus introduces a new harmonic pattern or harmony that prepares the verse chords to transition into the chorus. For example, if a song is set in C Major, and the songwriter aims to get to a chorus that focuses on the dominant chord (G Major) being tonicized (treated like a "home key" for a short period), a chord progression could be used for the pre-chorus that gets the listener ready to hear the chorus' chord (G Major) as an arrival key. One widely used way to accomplish this is to precede the G Major chord with its own ii–V7 chords. In the key given, ii of G Major would be an A minor chord. V7 of G Major would be D7. As such, with the example song, this could be done by having a pre-chorus that consists of one bar of A minor and one bar of D7. This would allow the listener to expect a resolution from ii–V to I, which in this case is the temporary tonic of G Major. The chord A minor would not be unusual to the listener, as it is a shared chord that exists in both G Major and C Major. A minor is the ii chord in G Major, and it is the vi chord in C Major. The chord that would alert the listener that a change was taking place is the D7 chord. There is no D7 chord in C Major. A listener experienced with popular and traditional music would hear this as a secondary dominant. Harmonic theorists and arrangers would call it V7/V or five of five, as the D7 chord is the dominant (or fifth) chord of G Major. Chorus or refrain The terms chorus and refrain are often used interchangeably, both referring to a recurring part of a song. When a distinction is made, the chorus is the part that contains the hook or the "main idea" of a song's lyrics and music, and there is rarely variation from one repetition of the chorus to the next. A refrain is a repetitive phrase or phrases that serve the function of a chorus lyrically, but are not in a separate section