In single-trace fragility theory, forgetting is produced by two factors, time and interference. Memory traces are assumed to have two partially coupled dynamic properties, strength and fragility. Strength determines the probability of correct recall and recognition, while fragility determines the susceptibility of the trace to the time-decay process but not to the interference process. Consolidation is assumed to be a continual reduction in the fragility of the memory trace rather than any change in strength or availability. Decreasing fragility accounts for the continually decreasing forgetting rate, the temporal character of retrograde amnesia and recovery therefrom, and the type of internal clock necessary for nonassociative recency judgments. Data are presented to indicate that interference is independent of the interval between original and interpolated learning, that nonassociative recency discriminability approaches a limit at about 30 min, and that the decay rate of long-term retention in amnesic patients is the same as in normal Ss.