“It is true that scientists and doctors use the word clinically, and it is also true that patients and their loved ones don’t always know what to make of it, especially when they first receive the diagnosis. It is too imprecise, for one thing. Dementia can be a spectrum, ranging from mild to severe, and some of the causes of dementia are entirely reversible. Alzheimer’s disease, which accounts for more than half the cases of dementia, gets nearly all the attention, and as a result, the terms dementia and Alzheimer’s are often used interchangeably. They shouldn’t be. The word dementia, however, is steeped in our common vernacular, and so is the association with Alzheimer’s disease. In this book, I use both terms with the hope that the conversation, and the words we use to describe the broad condition of cognitive decline, will shift in the future.”