Well, the interpretations are based on a mixture of my own personal experience in what happens after I dream of those symbols, various psychological theories (Freud, Jung etc) and traditional interpretations based on ancient Greek/Latin writings which have been passed down. These writings are usually where the more 'direct' interpretations come from.
There are always going to be some differences in opinion as to what they mean, and they could vary from person to person depending on that person's experiences of life. For instance, if I went to Paris with a friend, both me and the friend would come back with different descriptions of Paris. I might describe the scenary or the food, and she could talk about the museums and the art galleries, but at the end of the day, despite different descriptions, we are talking about the same place.
And like with the MMR debate, for every handful of doctors who say it's safe, you get another handful of doctors and parents who say it isn't. There is always going to be disent about everything
AND another thing I forgot to mention, is that dream interpretations can take YEARS before they materialize. Most of my own prophetic dreams happen within 6 months of me dreaming them, and some a few days after, but the longest time span I've ever had for a dream to come true is 5 YEARS.
I dreamt of my wedding dress in it's exact detail, 5 years before my wedding day, and before I even realised who my future husband would be. I should add that my wedding dress is very distinctive in detail, and is PINK, not white so it's not hard to mistake. I dreamt of this pink dress with all the same details when I was 13, and wrote it down in my diary. Then 5 years later at 18, when I was planning my wedding to Andy, I saw the dress in a Bridal store sale. It was end of line (only 1 left) and in my exact size. I realised it was the same dress from my dream.
So you could think that something isn't going to happen, but maybe you're expecting it to happen quickly, and they don't always
I thought I'd put some of my dream diary on here so the skeptics can see what I mean, LOL.
