For pianists, play the
X chord with the right hand and the
Y bass note with the left hand. For guitar/bass bands: guitarist plays the
X chord and bassist plays the
Y bass note. (With thanks to @piiperiReinstateMonica)
There are three main parts to this answer that can be read independently of each other.
- What does it mean? (includes subsections on literal interpretation and contextual meanings)
- Literal meaning
- Contextual meaning
- How does one play it?
- Other slash uses
- Secondary dominants
- 6/9 chords
- Further reading / Related questions
What does it mean?
Chords of the form
X over Y, and sometimes called "slash chords", mean
play chord X, making Y the lowest note.
For example, the first of the "Queen chords",
play a Bb7 chord, and make the lowest note a D.
Similarly, the second chord in "Can't Help Falling in Love", means
play a C major chord, but make the lowest note a Bb. Note that
Bb is not part of a
C major chord (which contains pitches
C E G). This is address below in the "How does one play this?" section.
X includes note
Y, then you're looking at an inversion of
X. For example
C/E is a first inversion
C major chord, played
Cm7/Bb is a third inversion
Cm7 chord played
Passing movement in the bass
Sometimes you want the bass to move smoothly from one chord to the next. Consider the "Can't Help Falling in Love" example in the OP. The basic chord sequence is
Bb - C - F - Gm. If taken literally, the bass player would play only the chord roots:
[V:v1 clef=bass] "Bb"B,, "C"C, | "F"F, "Gm"G, |
However, the chord notation is letting the bass player know that a descending step-wise pattern is wanted.
[V:v1 clef=bass] "Bb"B,, "C/Bb"B,, | "F/A"A,, "Gm"G,, |
Sometimes you want chord to change above a stationary bass pitch, known as a pedal tone The "On Green Dolphin Street" example in the OP demonstrates this. The
C is kept in the bass through the entire first four bars while the principal chords change above it.
Sometimes it's easier for the music reader if the chord notation uses slashes to clarify or simplify things. For example, "On Green Dolphin Street" might have been notated
Cmaj9 Cmin7 D7 Dbmaj7. This would be literally correct as far as the notes involved, and an astute player, or one familiar with the tune, would recognize the possibility of the C pedal tone (see #3 above).
However, that's more complex to read than
Cmaj9 Eb/C D/C Db/C, which mainly involves triads plus a bass note, and the
/C chords make the pedal tone explicit.
How does one play it?
In literal terms, this is answered above: you play chord
X, placing (or adding)
Y as the lowest pitch. In essence, you can play chord
X however you want (that is, in any voicing), as long as
Y is the lowest pitch.
In practice, this depends on the context you're playing in. If you're a soloist or otherwise responsible for the bass line/lowest pitch, then you make sure
Y is the lowest note. But if you are playing with a bass player, or some other instrument responsible for the lowest part, then you probably want to avoid playing
Y -- at least not in the same octave as the bass part -- so as not to conflict. (This is a rule of thumb, but not a rule. For more on that, see this question: Should the comping instrument ever double the bass player?)
So, for example, given a
G/B chord, if the bass player has the
B, then the piano or guitar would play
D (and possibly
B), pitched higher than the bass's
Other slash uses
In Functional Analysis (Roman Numeral Analysis), slashes are used to indicate a secondary dominant relationship. Secondary dominants are explained in What is a secondary dominant chord?.
There is another form of "slash" chord in which a horizontal line is used, and the notation is written vertically. This denotes a "polychord". See also John Belzaguy's answer to the question Chord Symbols in Kurt Rosenwinkel transcriptions
The 6/9 chord is a pentad with a major triad extended by a sixth and ninth above the root, but no seventh. (Wikipedia)
In this case, the slash is just a separator for readability.
Related questions / further reading
Questions related to slash notation are reasonably common on SE:MP&T. Here's a compendium.
"What does it mean?" questions.
"How to play it?" questions.
Also of interest