Novelists, magicians, and other tricksters keep these words busy. Novelists love an allusion, an indirect reference to something like a secret treasure for the reader to find; magicians heart illusions, or fanciful fake-outs; but tricksters suffer from delusions, ideas that have no basis in reality.

Blink and you’ll miss it: an allusion is a quick indirect mention of something. It’s a literary device that stimulates ideas, associations, and extra information in the reader’s mind with only a word or two:

Littlemore was not quick at catching literary allusions. (Henry James)

Thomas Paine’s writings contain several affectionate allusions to his father, but none to his mother. (Daniel Moncure Conway)

Magicians love to create illusions, or visual tricks, like making a tiger disappear or sawing a person in half. Your eye can be fooled by an optical illusion, and Dorothy and the gang get to the bottom of the Wizard’s illusion and discover he’s just a regular guy. Illusions aren’t always glamorous; sometimes they’re just hiding the man behind the curtain:

“We have no illusion that these credits are going to create lots of new jobs,” the editorial said. (New York Times)

But while investing in your company’s stock might feel safer than betting on the stock market as a whole, that is usually an illusion. (Seattle Times)

Delusions are like illusions but they’re meaner. A delusion is a belief in something despite the fact that it’s completely untrue. Hence the phrase is delusions of grandeur. People with delusions often wind up on the shrink’s couch. Whether you are trying to deceive yourself or someone is trying to deceive you, if you believe the false idea, you have a delusion about reality:

Delusions are closely allied to hallucinations and generally accompany the latter. (Samuel Henry Prince)

Two medical experts had concluded then that the accused gunman suffered from schizophrenia, disordered thinking and delusions. (Reuters)

“Basically, I think he’s suffering from delusions of grandeur,” he said. (Chicago Tribune)

An allusion shows up in art, while illusions love kids’ parties. If you believe something despite reality, you have a delusion.