Two-note combinations, whether referred to as chords or intervals, are called "dyads". In the context of a specific section in a piece of music, dyads can be heard as chords if they have the most important notes that identify a certain chord. For example, in a piece in C Major, after a section of tonic C Major chords, if a dyad containing the notes B and D is played, listeners will likely hear this as a first inversion G Major chord. Other dyads are more ambiguous, an aspect that composers can use creatively. For example, a dyad with a perfect fifth has no third, so it does not sound major or minor; a composer who ends a section on a perfect fifth could subsequently add the missing third. Another example is a dyad outlining the tritone, such as the notes C and F# in C Major. This dyad could be heard as implying a D7 chord (resolving to G Major) or as implying a C diminished chord (resolving to Db Major). In unaccompanied duos for two instruments, such as flute duos, the only combinations of notes that are possible are dyads, which means that all of the chord progressions must be implied through dyads, as well as with arpeggios.