In sum, then, Reid argues that the both Lockean and Humean versions of RTM fail because (a) they presuppose a more robust variety of memory than they can allow for, (b) they fail to shed light on the nature of memory because of (a), (c) the accounts they do offer are satisfied by many things that aren't memory, and (d) finally, they lead to skepticism about the past.  Each of these points is well-taken and taken together seem more than adequate reason for rejecting Locke's and Hume's accounts of memory.