Early theorists divided memory into short- and long-term stores (Atkinson & Shiffrin, 1968) based on evidence of seemingly different properties. For example, short-term memory was theorised to be affected by recency and long-term memory by primacy effects. Later models refined this modal model to produce a working memory model (Baddeley & Hitch, 1974), although more recent theories favour a single memory system.
Although lots of research has focused on the distinction between memory structures such as STS and LTS, the more fundamental issue is how memory operates. Several factors at encoding have been proposed to influence whether material will be retrieved. The levels of processing model suggests that it is the depth of processing (in particular processing meaning) that influences how well material is remembered. The phenomenon of context-dependent memory demonstrates that the cues available at encoding aid retrieval; it is thought this is because they are stored along with the material being encoded.