ABSTRACT
One lesson one might take from this is that backwards causation is impossible, and so does not occur: if the possibility of backwards causation leads to paradox, then backwards causation cannot be a possibility after all. A less hardline response is to say that, whilst a scenario where you kill your grandfather is impossible, this does not mean all scenarios involving backwards causation are impossible. So you can time travel, but if you attempt to kill your grandfather you will be thwarted in some fashion. Perhaps your gun misfires; perhaps you kill a man you thought (mistakenly, as it turned out) was your grandfather; perhaps in your haste to get to a good vantage point you slip on a banana peel and sprain your ankle (see Lewis 1976 and Smith 1997).
