I've been thinking about this for some time. I never really considered the "Blues scale" to be a proper scale. I've always thought of it as a pentatonic scale with a chromatic note placed between the 4th and 5th degree. It seems, though, that some people consider the blues scale to be a scale all of it's own. This has led me to think that the blues scale is not part of tertian harmony, because I cannot find a way to harmonize the chromatic note to a relative 3rd. If you were to harmonize the F# in a C blues scale to a major 3rd, you will get a Bb, but that's already the relative 3rd of the 5th. If you harmonize it as a minor 3rd, you will get B, which isn't even in the C blues scale. What are your thoughts on this?