Modes give another musical 'feel' to a solo. You may play in one Key Signature, then use a Mode to sharp or flat the notes, in a certain sequence, to change the sound. The sequence is based on a Major Scale Key Signature. As a Lydian Mode example, let's use the root D in the DMaj scale:
The Lydian Mode uses the 4th note of another Major Scale, as its own root. Above, we're using D as the root, so we must find what Major Scale has D as its 4th, note. In other words, from what Major Scale can we play the D Lydian Mode?
Let's think backwards, and start at the letter D. Count back from D four letters:
So, the A Major Scale has D as the 4th note, the Lydian Mode root note. This Lydian Mode retains the same Key Signature as the A Major Scale. The Key Signature is:
Therefore, the Lydian Mode, with D as the Root, is:
We may use this Lydian Mode to solo over the original Key we were playing, D Major:
We see that in order to find our Lydian Mode, we must:
Switching between the natural 4th note, and the sharp 4th note, changes a song's sound, and therefore feeling. Changing other notes gives us different Modes. To remember the Modes easier, use a Major Scale, and change (sharp or flat) notes to make a Mode:
|Lydian||1 2 3 #4 5 6 7 8|
|Ionian||1 2 3 4 5 6 7 8|
|Mixolydian||1 2 3 4 5 6 b7|
|Dorian||1 2 b3 4 5 6 b7 8|
|Aeolian||1 2 b3 4 5 b6 b7 8|
|Phrygian||1 b2 b3 4 5 b6 b7 8|
|Locrian||1 b2 b3 4 b5 b6 b7 8|
Use this chart for any Major Key. We only need to know the starting Root. Also, a sequence develops as you add the next Mode:
Numbering between each addition, is a rollercoaster:
This is just a shortcut to memorize the sequence of added note changes for Modes. The Modes' names themselves, in this particular order, may be remembered with an acronym:
The #4 Lydian, and the natural Ionian are unique modes. The others flat one or more notes of a Major Scale. Listen to the sound of a mode to easily memorize and find it within a key. Our ears may be trained if we focus on sound.
Another way to look at modes is to see them in their own Major Scale. All of the modes just start on a different letter. Their root is new, but the key signature is the same as the Major Scale they started from:
Start with any Major Scale, and you may find the Mode you need by changing to another letter in that scale, and keep the same key signature.
Recommended reading: Guitar Tab and NotesMaterial by Eleventh Decibel.