I'm not sure who said that the unconscious couldn't understand negation, but it wasn't Milton Erikson. He used direct negative suggestion, such as, "you don't have to keep your eyes open" when he wanted someone to close their eyes.
The key isn't so much that "the unconscious doesn't understand" as it is "the non-verbal portions of your brain deal with information coded in ways other than verbally." While more difficult to understand, this does show how the rules work. For example, "I can't tie my shoes" brings to image __________. While "I can't see you building your own car from spare parts" brings to image __________.
See how it works?
Can't is a VERY dangerious word, because it is magical. It's magical in the sense that "magic" deals with things outside of normal laws of nature. In the normal workings of nature, all things have a temporary nature. It is up to philosophers to determine if this temporary nature is linear or cyclical, but it does exist. If I were to say "I can't spell," I would be automatically limiting my abilities to learn from watching spell-checkers and PhotoReading. I would be accepting a condition which is essentially UN-BOUNDED in time and will persist at least as long as I do. If I were to say, "I am not currently able to spell," I would be saying something true. HOWEVER, I wouldn't be implying that I will NEVER be able to spell.
