Watch the Over A Blues online guitar lesson by Rob Garland from The Guitarist's Pentathlon

A popular application of the minor pentatonic scale is using it to play over a blues. Tension comes from the b3rd in the scale rubbing up against the major 3rd of the I chord. In the context of an A7 blues listen to the sound of the minor 3rd of the scale (C) as it hits up against the major 3rd of the I chord, A7 (the note C#).