In this picture, as well as countless others: http://en.wikipedia.org/wiki/Image:NPN_BJT_Basic_Operation_(Active).svg we have electrons flowing from emitter to base, and 'holes' from base to emitter. Why the distinction? When an electron flows from emitter to base, is it not the same thing as a hole flowing from base to emitter? Holes are just a 'technique' to quantify electron flow, correct? Also, my book states this verbatim: "If the concentration of electrons in the n-type emitter is much larger than the concentration of holes in the p-type base, then the number of electrons injected into the base will be much larger than the number of holes injected into the emitter." Not understanding how they are distinct components. Thanks for any help guys.