Pain has been the focus of philosophical speculation and scientific attention since earliest recorded times. Yet, despite its history, advances in knowledge of neurophysiology and biochemistry, and the development of potent analgesic medications and sophisticated invasive modalities that have evolved, pain relief remains elusive. On average fewer than 50% of patients obtain at least a 30% reduction in pain following treatment with potent medications, pain reduction following rehabilitation averages around 30% (Turk, 2002a). Pain remains a perplexing and challenging problem for pain sufferers, their significant others, healthcare providers and society.

Although pain is an almost universal experience, there is little consensus even with regard to how to define it. Historical debates have raged back to the time of the ancient philosophers as to whether pain was a purely sensory or uniquely affective phenomenon. Arguments have persisted and the conceptualization of pain has more than philosophical consequences; it will affect how pain is assessed and how and even whether pain is treated.

One factor that has contributed to the debate about what pain is relates to the fact that it is a subjective experience. Unlike temperature, there is no ‘pain thermometer’ to determine the extent of pain that an individual has or should have. The only way to know how much pain someone has is to ask them and to make inferences from observation of their behaviours (see ‘Pain assessment’).