There is little doubt that within certain parameters, there can be evidence of the reliability of memory, and of its reliability in particular situations and among particular groups. Cognitive psychologists can test people's memory for associated word pairs, and determine under what conditions forgetting is more likely to occur. Such studies are not only intrinsically interesting (in part because we depend on memory for so much) but potentially very useful in helping us to know what to do to increase our ability to recall information when it is needed.  But as interesting and useful as such empirical studies are, there is reason to doubt their ability ever to show the general reliability of memory.