One property of dreams, which you have when you sleep, is that they are not real but imaginary, and thus may give you unlikely experiences.

In many languages throughout the world, not limited to English, you express your wishes you think are perfect (“ideal”), your ultimate desires, with the word “dream,” which means “an (unrealistic, unlikely, and impossible) imagination you get when you sleep.”

Why is that, despite those negative connotations?

  • Which negative connotations? Being unrealistic, unlikely or impossible do not in principle make something unwanted. – Keelan Jul 28 '19 at 9:32
  • Also note that in many psychological theories, actual dreaming reflects a persons wishes (see: en.wikipedia.org/wiki/Dream_interpretation#Psychology). So it is perhaps not surprising that "I dream of X" becomes "I would like X to happen". – Keelan Jul 28 '19 at 9:41
  • Also, in many traditions, dreams are not unreal, but are either predictions, or reflections of some supernatural world. – Colin Fine Jul 28 '19 at 11:23
  • 2
    I voted to close this question as a duplicate, but I (as usually) really don't understand the close votes with "language-specific" as a rationale, when the OP said very clearly that this semantic match happens "in many languages throughout the world", and that is what they are interested in, not specifically the fact English is one of those languages. I really wish use of that close reason were restricted to what it actually says, instead of being used as a sort of wildcard. – LjL Jul 28 '19 at 16:36

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