The Modes

If we play just the white keys on a piano from C to C, we will be playing the C major scale, this scales has a structure of 1+1+1/2+1+1+1+1/2 tones. But we can also call it the Ionian mode in relation to it's formula of distance between notes

If we then play a scale from D to D just white keys that formula will change to 1+1/2+1+1+1+1/2+1, this new mode is called Dorian, so we have a D Dorian.

Next we play from E to E just white keys, again the formula moves to the right one more step to 1/2+1+1+1+1/2+1+1, we have a E Phrygian.

From F to F another major scale with the tones has such 1+1+1+1/2+1+1+1/2, this one is the F Lydian scale.

Moving on from G to G, again just white keys a G mixolydian, and the formula 1+1+1/2+1+1+1/2+1. Beginning on the A and ending on the next A we get an A Aeolian scale, that goes 1+1/2+1+1+1/2+1+1.

And lastly the B Locrian scale and the formula 1/2+1+1+1/2+1+1+1.

I call them scales because has soon as you give it a tonality name it becomes a scale not just a mode. So for example C Ionian is both a scale and a mode, the scale is C and the mode of that scale is Ionian.

Each mode can be assigned with the roman numeral that is also associated with the respective chord that goes with that mode.