The terms can be confusing. But Alzheimer’s and dementia are not two different diseases. Dementia, in fact, is not a disease at all, but a syndrome, which means a collection of symptoms: trouble with memory, language, visual perception, and the ability to focus that is severe enough to interfere with daily life. Dementia can also include personality and mood changes and even hallucinations. The clearest way to understand the two terms is to say that Alzheimer’s is a disease that causes the symptom of dementia.