Dementia, being a syndrome, is defined entirely on clinical grounds. Table 13–2 lists the four critical elements of the definition. Dementia is a condition that affects cognition, which is defined as the mental processes used to obtain knowledge or to become aware of and interact with the environment. These processes include perception, imagination, judgment, memory, and language, as well as the processes people use to think, organize, and learn. For the dementia syndrome to be present, several areas of cognition must be affected (global). To differentiate dementia from mental retardation, the cognitive symptoms must represent a cognitive decline for the individual. The decline must be significant, typically sufficient to affect the person's daily functioning, operationalized as instrumental or basic daily living activities. Finally, because delirium can cause the full range of cognitive symptoms associated with dementia, it is critical that the cognitive syndrome be present in the absence of delirium. This broad definition has been operationalized in several criteria, with those of DSM-IV-TR (American Psychiatric Association 2000) being the most commonly used.