Blues and funk have their roots in African music. We are taught about the “blue” notes and there are various ” blues scales ” but this is of little practical value. ( see the end of this article for a suggested practical blues scale/major pentatonic combination)
Most African music uses a pentatonic scale but within that scale some of the intervals are very flexible. This varies across the continent, but in most regions the third covers a range from our minor third, through the major third , and sometimes all the way to the b4! The singers and musicians in these areas will play with microtones, bending and slurring the notes.
Reference “Africa and the Blues ” Gerhard Kubik
I like to call this the “ambiguous 3rd”. If the key is major you can use both the major and the minor 3rd, or use no third!
Here are some examples