Discussion Groups / English Usage / November 2006

Hi,

I have a question to ask about interchanging the words "illusion" or
"allusion" after I was reading some writing today on an internet
message board.     I was curious if I'm understanding the terms in the
correct context.

I read something along the following lines:

"I visited you today because I was under the allusion that we were
friends."

In the context of this sentence, is the use of the word "allusion"
correct?    My first thought reading the line was that the writer
should've used "illusion" instead of "allusion".   It seems that a lot
of people swap the two words often without thinking too much about it.
  Would it ever be correct to use 'allusion" in this context or one
very similar?  

thanks