No such argument from present ideas to past reality is available, for the same reason that no argument from ideas of sense to external world reality is available

Reid argues that for exactly similar reasons, the RTM leads to skepticism about the past. If we begin with the thesis that in memory all that one is aware of are ideas, then in order to justify beliefs about the past one will have to provide an argument with premises about our present ideas and a conclusion that the past is how we remember it. But there is no more reason to think that such an argument will be forthcoming than there is for thinking that on the basis of our ideas of sense we can