Ionian Mode (W-W-H-W-W-W-H) In this definition, W stands for
'Whole Step' and H stands for 'Half Step'. The Ionian mode defines the
familiar major scale pattern we hear as do, re, mi, fa, so, la, ti, do. The
half step between Ti and Do gives the scale some tension and release. The
majority of popular songs are written in the Ionian mode.
Dorian Mode (W-H-W-W-W-H-W) Dorian mode is most commonly heard
in Celtic music and early American folk songs derived from Irish melodies.
Songs written in Dorian mode sound a little melancholy because the final
note (re) doesn't quite resolve itself. The song may be over, but the singer
is still unsettled.
Phrygian Mode (H-W-W-W-H-W-W) Modern composers and guitarists
commonly use Phrygian mode because it works well with the Ionian. Guitarists
use modal music to create interesting solo lines which can be played against
melodies in other modes. Composers often find the Phrygian mode to be as
useful as the traditional minor (Aeolian) scale, but without the inherent
sadness. The theme of the animated cartoon The Simpsons is written in
Phrygian mode, for example.
Lydian Mode (W-W-W-H-W-W-H) Lydian mode is the complete opposite
of the Ionian, so it feels as solid as a major scale but the intervals are
surprising and unexpected. This is a popular mode among jazz musicians who
enjoy using a mixture of major and minor chord progression in inventive
Mixolydian Mode (W-W-H-W-W-H-W) Mixolydian is similar to Lydian
in the sense of a major scale feel with minor intervals. Mixolydian mode is
another popular scale for solo musicians looking for a counterpoint to the
Ionian key of the song.
Aeolian Mode (W-H-W-W-H-W-W) Aeolian mode is still in vogue
today, although we tend to refer to it as the minor key. The intervals of
Aeolian mode create the same feel as many modern blues songs. Songs composed
in Aeolian mode have a strong sense of sadness. The final note of an Aeolian
scale feels resolved in a completely different sense than the Ionian. If the
Dorian mode reflects melancholy, the Aeolian reflects despair.
Locrian Mode (H-W-W-H-W-W-W) Locrian mode is considered to be so
unstable and unsatisfying that most composers consider it unworkable. There
are few songs written in the Locrian mode, which has lead some music experts
to label it a 'theoretical' mode. It exists because all seven notes of the
Ionian scale could form modes in a mathematical sense, but the relationship
between intervals in the Locrian mode is simply not that interesting
borrowed from http://www.wisegeek.com/what-are-the-seven-modes-of-music.htm