I'm gonna say what I've learnt until now in my psychology course in college, in my brazillian's english. ;P
When we say there is an unconcious or subconcious mind, we have to say there is a conscious or subconscious mind, and there are people who say there isn't a conscious mind - like in behaviourism. It doesn't mean you don't think or feel, it's just that behaviourists doesn't admit the separation between mind and body, they say thought and feeling are behaviors of the organism. So, if you don't have that "mind" thing, you can't have an unconscious mind. I believe there are some things we do we aren't aware of, or we do but don't know the reason, but I wouldn't say that we do it because the unconscious said we should do it. My guess it that some of our actions might be the result of stuff we learnt through our lives but just aren't aware of (yet).
The behaviourist philosophy of psychology is theory that is different from those called "mentalists" - these say there
is a mind, and they study it. There are other philosphies in psychology...
Psychology is different from psychoanalysis!!
Psychology, as a science, focus the study in what can be seen or studied directly (but I leave the discussion about what can or cannot be studied directly to some other day...), so it may study the mind, like cognitive psychologists do (or not, in the case of the behaviourists). Psychoanalysis (that one from Freud) is not exactly psychology, since psychoanalysis has as axiom that
there is the unconscious and our behaviours are largely determined by it, and the unconscious
can't be studied directly. Freud made his theories based in the existence in this thing he called
unconscious. He invented that term. He was a doctor, and in his clinic, when studying the most weird cases at his date, he thought there must be something hidden that determined people's behaviours, so he called that unconscious. But that's what Freud said, it doesn't mean it is
the truth. It's what he said - and his theories are still being used, still working in some cases, not working in other cases, and are subject of lotssss of discussions.
Jung also believed in the unconscious, and MBTI is based in his theories.
About accessing the unconscious by introspection, Wikipedia says: "Unconscious thoughts are not directly accessible to ordinary introspection, but are supposed to be capable of being "tapped" and "interpreted" by special methods and techniques such as meditation, random association, dream analysis, and verbal slips (commonly known as a Freudian slip), examined and conducted during psychoanalysis." (according to Freud...)
I just tried to simplify some things a little, so it's lacking some stuff...
But I guess I'm leaning more to the behaviorist side, and I may work with behaviorism in the future... So I think there isn't an unconscious mind - there are just things we aren't aware of, or something like that... I'm not sure of my opinion, I'm still in the first year of college!
One thing that everyone agree about that is that all your memories that you arent thinking at the moment are unconscious, then when you think of them, they come to consciousness for a brief moment and go back to unconscious.
I dont see whats even the point of asking if unconscious exists or not, because memories that arent in your consciousness at the moment still do exist, so unconscious is pretty self evident.
Freud made these three concepts: conscious, preconscious and unconscious mind. Those things we remember at the moment are conscious; when we aren't thinking about them, but we can recall them anytime are in the preconscious. The other thing that determines us is the uncounscious.