Mode Parent Scale Concept
Books on Modes
This is a simple table of the parallel modes of A Major. The parallel modes 'visit' other scales.
A Major Ionian - Is the same as A Major regardless if parallel or relative / Derivative
A Major Dorian - Finds the scale where the A note is the 2nd tone of the scale. This would be G Major.
A Major Phrygian - Finds the scale where the A note is the 3rd note of the scale. This would be F Major.
A Major Lydian - Finds the scale where the A note is the 4th tone of the scale. This would be E Major.
A Major Mixolydian - Finds the scale where the A note is the 5th tone of the scale. This would be D Major.
A Major Aeolian - Finds the scale where the A note is the 6th tone of the scale. This would be C Major.
A Major Locrian - Finds the scale where the A note is the 7th tone of the scale. This would be B flat Major.
The parallel modes visits other scales outside of the A Major scale. This is the opposite of the relative or derivative modes that only use the notes of a single Major scale.

C Ionian
D Dorian
E Phrygian
F Lydian
G Mixolydian
A Aeolian
B Locrian
All God's children have names. All modal children have names. C Major is the parent scale because when you are playing D Dorian, you are playing the very same notes as C Major. When you are playing E Phrygian, you are playing the very same notes as C Major. When you are playing F Lydian, you are playing the very same notes as C Major. And so it will continue to be as you step through all of the other children of the parent C Major Scale. All of these child modes owe their existence to the hard working C Major scale. D Dorian would not exist without the C Major scale and so forth.

The answer is the whole step / half step pattern changes when you start on a different note within the scale. Please review the diagram below for a visual representation.
Playing relative modes…
All the notes of C Ionian are found within the parent scale of C Major. <—That should be a given.
All the notes of D Dorian are found within the parent scale of C Major.
All the notes of E Phrygian are found within the parent scale of C Major.
All the notes of F Lydian are found within the parent scale of C Major.
All the notes of G Mixolydian are found within the parent scale of C Major.
All the notes of A Aeolian are found within the parent scale of C Major.
All the notes of B Locrian are found within the parent scale of C Major.
All the notes of C Ionian are found within the parent scale of C Major.
There is a meaning somewhere here.
An example or three:
G Mixolydian is NOT found within the G Major scale.
D Dorian is NOT found within the D Major scale.
A Aeolian is NOT found within the A Major scale.
The three examples immediately above are found within the C Major scale. Review and review until this is clear.
The overall tonality of the scale changes when you change the step pattern by beginning on a different tone within the scale.
Whole and Half Step Pattern Changes Within the Modes
