A major scale with altered 3rd and 7th degrees involves raising or lowering these specific notes to create different harmonic colors and tensions. For instance, raising the 3rd (from a major to an augmented third) can create a brighter sound, while lowering the 7th (to a flat seventh) introduces a bluesy or dominant feel. This alteration can be used in various genres to add expressiveness and complexity to the music, often resulting in a more nuanced emotional palette.