Blues Scales
Formula: R - b3 - 4 - b5 - 5 - b7
Blues scales are commonly used to solo over Major & minor blues, & over minor chords in general. Blues scales create a 'bluesy' feeling, or an 'earthy' quality. It is commonly used by Rock, Jazz, Blues, & R&B players.
Play through each scale. Improvise within the given octave in any position. There are numerous ways we can finger each of these. The 7 octaves are our starting point.
We can use the G blues scale to solo over G blues. In this instance, we are making a single scale choice for an entire harmonic progression. When playing a blues scale (the minor pentatonic with the b5) over G Major blues (G = I, C = IV, D = V), we may hear some 'clashing'. It is common to make modifications [mods] to the scale to match up the sounds.
One modification is adding the Major 3rd to the scale while the G (or G7) is sounding, then just playing G minor pentatonic over the C chord, & adding the F# while the D is sounding. At some point with the V chord, we have to make so many mods, it might just be better to use a different scale. We have choices (even in how we think about all of this). Another option is to switch to each of the corresponding blues scales for the given chord root. When playing blues in G Major, play G blues scale with the G chord, C blues scale for the C chord, & D blues scale over the D chord.
Keep in mind that the 'blues' scale is a minor scale, so it can be called the minor blues scale. When we add the Major 3rd to the blues scale, we can call it the Major b3 Blues scale. Another option for Dominant type chords (G7, C7, D7), it to use the corresponding Mixolydian (Major scale with a b7).
The flat 5 is also the sharp 4 (the tritone - 3 whole steps - 6 half steps) & can be named the # name as in some of our notated examples. This tone acts as a passing tone, not a strong beat tone. It can occur as a connection tone between the 4 & 5 within the melodic motion. For minor type chords, the blues scale is a good fit. It is also common to alternate between the Dorian mode (R-2-b3-4-5-6-b7) & the blues scale for the minor.