Dreaming of Signs
I realize this post is two days late, but I felt it necessary to post something, albeit brief, about the dream sugiyot.
One persistent theme I found almost throughout is the connection between dreams and the importance of language and signs (apologies to all you semioticians out there who don't distinguish between the two).
Some schools of thought believe that thought comes before language. Meaning, people have thoughts and think of images, and language is a pale reflection of those thoughts. In the past few decades, theorists have come to believe that thoughts are framed by language, and there is thus no point in trying to get behind one's language and culture in viewing one's "true" thoughts, because ha beha taliya, one's ideas cannot be separated from language and context.
Our sages in the sugya on dreams seem to take this second view of signs and language. Frequently in the sugya, images are interpreted using verses in the Bible, suggesting that both donkeys and biblical texts are interchangeble. Both are signs, and thus the image of the ox can easily be interpreted using another verse that mentions oxen.
Similarly, interpretations of dream can be interpreted not only based on the object itself, but also the Hebrew name for the image. In fact, in one spot, we are told that when one views a can in a dream, its interpretation can depend on whether one pronounces its Aramaic form as Shinra or Shunra. Language and image become intertwined.
On 55b, R. Yonatan states that a person is only shown products of his/her own thoughts. Rava proves this by noting that people never see a palm tree of gold in their dreams because they never think about such images. These passages suggest that even if dreams are divinely influenced, they can never be detached from language and culture.
I think the most apt metaphor for a dream in rabbinic thought would be a text. Dreams, like texts, can be interpreted in different ways, and their meanings end up following their interpretations, rather than having an "objective meaning. Even the image guide mentioned later in the sugeya (like about someone who dreams about barley, etc.) can be seen as instructions about how to view a dream positively. (This would explain why that passage even views a death as a positive dream.) As in Torah sheba'al peh, the mouth ends up as the prime interpreter of the text, which explains the literal meaning of the statement that dreams follow the "mouth."
Like texts, dreams can be interpreted differently based on the different intertexts (parallel texts) that they are compared to. This explains why, towards the beginning of the dream sugeyot, the Gemara gives advice for what one should do after seeing various images in a dream. For example, if one sees a river in a dream, he/she should recite (notice the verbal aspect) a verse with a positive mention of a river before he/she thinks of a verse with a negative mention of a river. One must interpret the dream positively by relating it to a positive intertext, pushing the dream in a positive direction.
This comparison would explain why meanings of a dream can be flexible, even if they can be prophetic. Heaven gives us the text, it is our job to interpret it and make the best of it.