In Chapter 1, we noted that learning focuses on the acquisition of knowledge or a skill, whereas memory refers to our capacity to later recall it. We also noted, however, that the two concepts are intimately, perhaps inextricably, intertwined. Learning necessarily involves memory: To show that you have learned a king's name during a history lesson, you must be able to remember the name. Conversely, memory depends on learning: You can only remember the king's name if you learned it in the first place! In essence, learning and memory are two sides of the same coin – that certain experiences have enduring effects on our behavior – and which term we use depends largely on whether we are emphasizing the initial impact of the experience (learning) or its subsequent effect (memory). Having emphasized the first aspect in the preceding chapters, we now turn our attention to memory.

We are so good at remembering things that we tend to take this achievement for granted. If someone asks you your telephone number or what you ate for breakfast, you could answer immediately, and the ease with which you do so can make it hard to see what a remarkable phenomenon this is. In the course of your life, you have stored a huge amount of material in your brain – a vast number of experiences with families and friends, the meaning of perhaps 80,000 English words, the physical movements required to ride a bicycle or talk, and so on. Given this enormous number of stored memories, how do we retrieve the information we want so effortlessly?