In my personal studies in philosophy I have come across a the words "illusion" and "delusion" quite a few times, and for my own interests I would like to figure out how they may be distinguished more precisely. For quite a while I had been looking for a word that captures the idea of believing in something simply because you want to believe it, regardless of whether or not it is true. This must be distinguished from simply believing in something that in actuality is or isn't true. Then I ran across the word "illusion" used in this way by Freud on a number of occasions, and he distinguishes the word in the same way from being what he calls "delusion". So I went to the sacred OED, and in spite of my diligent searching, I could not find support for Freud's use of the word in this manner. I am hoping that one of you linguiphiles out there may be able to help me out here. I would love to adopt this sense of the word for my own usage, but I do not want to confuse or frustrate every reader who may read my work in the future. So tell me, is Freud the only one who has used these words in this way? Even if he is, I'm afraid I'll still have to adopt this usage, because I can't find any other word that captures the idea so well.