The purpose of this writeup is to present the theory of operation behind Dianetics. Whether or not you believe it is up to you.
As fair disclosure, I am what you might call a Dianeticist. I believe that the Dianetics model of the human mind is accurate, and that Dianetics processing, done properly, works. I am not a Scientologist, although the two are not mutually exclusive. All Scientologists can be considered Dianeticists, but not all Dianeticists are necessarily Scientologists. In other words, Scientology pre-depends on Dianetics, not the other way around.
The basic premises are that:

Dianetics, which is from Greek words and means, roughly, "through the soul," or "what the soul is doing to the body," is a science of dealing with past trauma in order to restore full cognitive ability in the individual going through Dianetic processing. The book, Dianetics: The Modern Science of Mental Health, was released in May of 1950. Hubbard's further researches led to the advent of Scientology a few years later. Scientology is described as "an applied religious philosophy" - and one which I do not fully understand, and which is beyond the scope of this article anyway.

The Dianetic model of the human mind describes the following elements:

  • Analyzer - The decision-making part of the mind. Barring physical damage, it is incapable of making an incorrect evaluation based on the data it is provided from the senses and from memory. (If it is provided with faulty data, its answer will reflect the faulty data. In this case, it has not erred, but something like a GIGO condition has occurred.)

  • Standard Memory - This is where all conscious memory is stored. If movie film could record more than 50 perceptions simultaneously and perfectly, it could be said that standard memory was like movie film. The analyzer draws on standard memory when making decisions.

  • Engrams - When an organism is subjected to pain, be it physical or mental, all of the perceptions present in that moment, including what was said, are recorded not into the standard memory, but into engrams. Depending on the amount of pain present, some or all of the engram may be occluded from conscious recall. When conditions similar to the ones in the engram reoccur, the engram may be re-stimulated.
    In this case, it will start feeding information to the analyzer, but the analyzer will be unable to see most or all of the memory itself; therefore, it will be receiving data out of context, and will return an answer consistent with that non-contextual data.

Engrams compose what is called the reactive mind. The reactive mind thinks in identities - everything in the engram is equal to everything else in the engram. The analyzer, along with the standard memory, thinks in terms of differences.

The analyzer, along with standard memory, might provide the following synopsis:

Apples taste a certain way. Once I bit into an apple, and it had a worm in it. The rest of the times I bit into an apple, there was no worm. Apples may be red, green, yellow, or, in the case of a Gala apple, red AND yellow.
The reactive mind, however, might provide this synopsis:
Apples = Worms = The taste of apples = The sensation of biting into an apple = Discovering a worm in an apple = Apples = Worms = Discovering a worm in an apple = (etc.)
If you have an engram concerning finding a worm in an apple, it may cause you to find all apples repulsive, or perhaps just the thought of biting into an apple, even though you almost never find a worm in one.

Then again, you might not find apples repulsive at all, because the engram may not have been sufficiently restimulated to start dumping garbage into your thought stream.

A few of you may have seen that video on goofball.com of a toddler walking through a garden. Suddenly, out of nowhere, a cat pounces on the toddler's head, knocking the toddler to the ground. This is the sort of incident which causes people to hate cats, or just to feel a certain nervousness around them. There is no reason to hate or feel nervous about all cats because of something done by just one cat.

Racism is caused by engrams. There is no reason to hate an entire race of people because of the ill-doings of a few of its members. The racist will often echo the sentiment that "they're all alike" because s/he/it has lost the ability to differentiate the actions of one or several people from the actions of everyone with a similar appearance.

Engrams are particularly dangerous where they contain speech, because everything in them is interpreted literally. What is said in an engram can literally have as much force as something said to you by a hypnotist, who then tells you not to remember what went on during the hypnosis session. For example, I may hypnotize you and tell you to take off your jacket if I touch my nose, and then put it on again when I touch my tie, and then instruct you not to recall what was said in the session, then bring you back to consciousness. I can touch my nose and tie fourty times, and you will come up with any excuse imaginable why you are messing with your jacket - it's too hot, or it's too cold, or you're coming down with something, and what's wrong with the air conditioning anyway? If I then tell you that I programmed you to respond to me touching my nose and tie, the effects of those hypnotic commands are immediately destroyed.


Application

The process of Dianetics is called auditing. The auditor issues simple commands to the person being processed. The person must be fully conscious and free of drugs of any kind or it won't work, as the whole point is to restore occluded memories to the standard memory banks, thereby "removing" them from the reactive mind - and this can't happen when the person is going through sleep loss or under the influence of drugs.

As a result of the requirement of full consciousness, hypnosis is obviously out of the question. The book speaks rather poorly of hypnosis, citing it as being dangerous.

The person is asked to locate an incident which s/he feels comfortable facing. The auditor then instructs the person to mentally return to that incident and go through it, recalling as much as possible. This is done multiple times on the same incident, until no more data comes up; each time the incident is gone through, more and more of it is restored to standard memory, where it cannot subconsciously influence the person - but rather, can be evaluated properly and consciously against present conditions. At the end of that, the person either has a cognition - in other words, they come to a sudden, highly valuable, and sometimes euphoric, realization about themselves, and what they are REALLY capable of, and/or how things REALLY are - or the auditor instructs them to locate an earlier incident like the one being audited. (In that case, what was audited may be a part of a chain of engrams, or locks - which are periods in which an engram was restimulated, and when the "root" engram is discovered and fully restored to standard memory, that engram and all of the others after it in the chain lose their power to subconsciously influence the person, and a cognition results.)

Side-effects are said to include increased ability to recall things, a wider attention span (due to the fact that the engrams are no longer in restimulation and leeching cognitive resources), and a more cheerful outlook on oneself and of life in general.

There is more to it than that and I may update this later. I hope it provides an accurate view of the theory.