When it happens
Begins in mild dementia and continues into moderate and severe dementia
Why it happens
Problems with language -- known as "aphasia" -- start with damage to cells relating to memory. As the cells that are associated with the language and visual processing centers of the brain are damaged, the difficulty identifying objects and calling them by their right name progresses.
Words can be mixed up or made up ("thingamabob," "tooth shiner"). Making up words is also known as "apraxia".
What you can do
Avoid pointing out errors (which can't be helped), correcting the person in an obvious way, or making fun of him or her (even though some mix-ups can sound funny).
You can usually figure out what's meant by context: the situation and the rest of the words used.
Repeat the correct word, without drawing attention to it: "Your toothbrush is on the counter."