[Harp-L] 3rd position

[TomEHarp@xxxxxxx]

question,why   i'm looking through a book called blues harp and in the 
position section it says in 3rd posion f is not posible unless the guitar uses a 
capo??won't g harp work?? and in 4th g c and f are not posible unless a guitar 
uses a capo.