Blues scale
 

Hello Everyone !
I'm a student and I love music, blues in particular.
I also try to compose.

But I have a question for you,
I know that classic blues grid is, but I would like to know if we have to change the scale each time we pass from I to IV for instance.
I say that cause I play that on harmonica, and well, would like to know if I have to learn all 3 scales of blues.

In brief: Do we have to use for instance C blues scale, then pass to F blues scale and then to G blues scale (for the I, IV, and V) ?

You can do either. Some stay with a minor pentatonic based on the I chord for the whole chart, all 5 notes will work over the IV and V chord. Others change scale with the chord - or mix up both approaches.

With major and minor scales, chords fit into a scale so there is no need to change scales when changing chords. This is true on guitar and piano, however with harmonica they do things a little differently and have a little secret known as "cross harp."

Cross Harp vs. Straight Harp | Wildflower Harmonica Instruction
http://i66.photobucket.com/albums/h2...harpchart1.jpg

These have been the best answers I could have read ! Thanks a lot !
You are amazing ! =D

In a sense, yes you do. If you are soloing then you definitely need to know. 12 bar blues (I, I, I, I, IV, IV, I, I, V, IV, I, I) you need to know those scales and change between them. If you're going to hold a note over for a beat or two after the change, make sure it goes into the next key as well. Basically the same thing for composing.

Blues Scales
 

I only play the Pentatonic scale when I play blues.

Though I predoinately play lead guitar.

The key is to practice your scales consistently, then you will find the natural switches between chords.

I used to practice a lot with backing tracks and that helped me loads.