The pentatonic scale ? A, Am, D, Dm whats the difference and why ?

I played guitar in bands and solo for quite a while and I think you may be making things hard for yourself,just enjoy youself.Hendrix played a right hand guitar upside down so I do not think he worried about the pedantic reasoning behind his playing,he just let it flow and it is a pity he died so young as he was the most original player I have heard.