This article presents a defense of “presentist externalism,” that is, the claim that memory contents are fixed by the environment and by the time at which a recollection takes place rather than by those at which the original mental state occurred. Its case is an instance of an argument to the best explanation. The author argues, firstly, that “presentist externalism” is the only version of content externalism that can stand up to both Boghossian’s memory and fallacy arguments. In slow switching cases, inferences containing memory thoughts as premises are unsound or unsafe, but valid. The author contends, secondly, that the externalist must recognize the existence of wide mismemories besides wide forgetting and that only the presentist externalist can account for their existence. The author maintains, finally, that if the validity of an inference requires that all its premises and conclusion be evaluated in the same context, that in which the inference is made, then it is the present context that fixes the content and the concepts of memory rather than the past.