Where does Freud say, "The unconscious mind can only wish?" I've been tasked with either agreeing or disagreeing with this statement, but I cannot find exactly where Freud is said to have made this statement, thus no context.
Paco Mitchell at Depth Insights lists the following reference for “the unconscious can only wish”:
Full text is available at Archive.org. You may also want to search for "can only wish" on Scribd's copy of Jung's Freud and Psychoanalysis, and Archive.org's full text of William White's Mechanisms of Character Formation: An Introduction to Psychoanalysis. These provide plenty more context, though I'm not seeing a direct reference to the original source of the quote...
The "quote" seems not to be verbatim, at least not from Freud. Ferenczi (1910, p. 21) describes Freud's views of the unconscious with the words:
Others, like Kaplan (1917), von Geijerstam (1920), or Jung (see Nick's answer), have used similar phrases to summarize Freud's theory. The idea expressed in the "quote" must be older than Frenczi's publication from 1910, so it belongs to Freud's first "topography" of the psyche (Unconscious, Pre-Conscious, Conscious) and does not related to the second (Id, Ego, Super-Ego).
Whether Freud ever "said" or wrote the exact words like Ferenczi gives them, is unclear. I cannot find any variation of the phrase in Freud's published works, which proves nothing, only that he might have used slightly different words than I can think of. But then he might have actually said them – in a conversation or conference presentation –, or Ferenczi might mean that Freud's views can be summarized with this phrase.
Whatever the origin of the "quote", the important aspect in it becomes clear when we look at the context these autors put it in. Frenczi writes that
Wilhelm Reich (1928, p. 260), in a review, poses the rethorical questiion, if this is true:
So apparently the idea expressed by Freud is that not only can the unconscious not do anything else than wish, it also must wish, always.
Freud himself expressed his theory in the Interpretation of Dreams (1900, p. 573), where he writes of the unconscious,
With these hints I'll leave the rest of your assignment to you. We want to avoid that your teacher googles your essay and wants to give the course credit to me ;-) Find out about the origin of the unconscious, what it consists of and what it does, and the answer to your question should be apparent.