The If / Then approach to chords is a highly effective method for walking bass lines and bass solos.
When the notes are already taken care of for you, you can shift your focus on the aspects of music that really matter (rhythm, articulation, space, phrasing, etc…).
This chart outlines the scales and modes that work really well over these particular major chord types: C major 7, C major 7 (#5), C major 9 (#11), C major 6/9.
The If / Then Approach to Major Chords
To view this chart in FULL SIZE click here: http://www.mutantbass.com/images/charts/major-if-then.pdf
*Note: This chart already takes care of your note choices for major chord types. This is your chance to explore other aspects of music (rhythm, space, dynamics, articulation, tempo, phrasing, etc…)!