I'm not sure if this is generally thought to be the case, but it seems like any view that would suggest that human choices are completely free should be totally out of the question in debates about free will.
Whatever your view on free will (libertarian, compatibilist, hard determinist), it seems clear that certain external factors have some effect on our choices. Our genes, environment and upbringing have some effect on the choices we make. I assume most libertarians would agree (feel free to correct me).
(Take, for example, a drug addict. It just seems pretty incontrovertible that to some extent the addict's choice to take drugs is partially influenced by the neurobiological underpinnings of his addiction—even if he has some say in the matter via his freedom of will.)
So, my question is this: How do proponents of libertarian free will make sense of this "partial external determination" of our choices? Another way to put it: How do libertarians make sense of the notion that our choices—though technically free—are still "influenced"?