The ego, in trying to deal with the demands of the id, superego and external world, will invoke various defense mechanisms. Defense mechanism are techniques used by the ego to protect itself from anxiety and the threats that may rise from it. There are a number of different defense mechanisms, and the ego will often use a combination of them. There are several important things to know about defense mechanisms. First, they operate unconsciously, otherwise, they would fail to protect the ego from anxiety. Second, most defense mechanisms offer some sort of gratification in some indirect way, reducing id's demands. Third, defense mechanisms must distort reality to be effective.
One type is repression, which is the most primitive of all defense mechanisms. It involves the blocking of id impulses at the unconscious level. Freud saw repression as universal but extremely limited. The basic problem is that it fails to resolve the demands of the id, because no gratification occurs. Also, it can require significant amounts of mental energy to maintain the blockage against the increasing pressures for gratification. Maintaining repression can take up energy normally devoted to other things, and so the ego suffers from fatigue, but because repression is unconscious the ego is unaware why it is suffering from fatigue. For this reason, depression is seen by Freudians as extreme repression. There is also a very controversial idea that traumatic memories can be repressed and later recovered.
I think that repression is a very interesting concept, and I do believe that people repress traumatic memories or experiences, although I have doubts as to how strong one's mind can be in repressing things, and if when you repress something if it is completely in the unconscious mind. I also have doubts as to how long you can repress something for. As far as I know I am not repressing anything, but the irony of repression is that you would not know you are repressing something until it is recovered at some point in time. One example of repression however, is that sometimes children will repress incidents of sexual abuse.
Displacement is another type which involves redirecting drive energy from one object to a substitute object. It is a very common defense mechanism and is typically when the direct expression of the drives would be too threatening. The problem with displacement is that the substitutes are unrelated to the original object, and so involves a distortion of reality.
I think that displacement is a very commonly used defense mechanism. I know that I have used displacement before - sometimes if I get upset with someone of authority to whom I cannot retaliate, I will later take out the anger or frustration on someone else - a friend of a family member. Displacement can also be used in healthy ways - for example, I have one friend who has anger management problems, but when she bought a punching bag, she would go take her anger out of it instead of displacing that anger onto other people - her social life improved greatly and so did her upper body strength!
Identification is another defense mechanism which involves incorporating characteristics of a drive object into one's ego. Identification often occurs initially with one's parents, but more generally it occurs mostly with individuals who are either admired or feared. Sometimes, when we are unable to directly express impulses, we may adopt the guise of a figure in whom such impulses are acceptable. In extreme forms, the identification may replace the individual's own identity.
I think that almost everyone uses identification at some point during their lives. It is probably most common during one's teenage years, when people are still figuring out who they are in relation to their environment. I know that when I was younger, I identified with my sister because she seemed to be everything my parents wanted in a daughter - smart, athletic, friendly, involved and trustworthy. Because I also wanted to be accepted and loved equally by my parents, I identified with her. I now realize, however, that I am equally loved and accepted by my parents, even if I am not my sister - I have my own personality and I bring my own aspects to the family.
Rationalization is another defense mechanism that involves offering an acceptable reason for behaviour in place of the true reason. This new reason is acceptable to both the ego and other people (the external world). "White Lies" is an analogy for this mechanism. Since rationalization prevents a person from recognizing the true motives for their actions, it represents a form of distortion of reality.
I think that people use rationalization as a mechanism more than anyone would like to admit - it is so much easier for us as humans to rationalize actions that we have "unacceptable" motives for. One example of a time that I have used rationalization is when I am procrastinating. To make an excuse to not work, I'll say, "well, I can only hang out with my friends until after dinner, and then I have to go back to dorm for study hall, so I can just hang out with them now because I will have to focus later."
A fifth type is Sublimation, which os when drive energy is redirected towards a socially desirable creative activity. While sublimation is useful, because it results in a valued product, it is also limited because the gratification cannot fully satisfy the demands of the id. Also, because it requires creative talent, it is not a workable mechanism for every individual.
I think that sublimation is a very interesting form of defense, and I believe it to be a very healthy expression of emotions and drives. I actually believe that without sublimation, many of the greatest creative masterpieces ever made would never have been created. Art, music, writing, you name it, is powered by emotion and experience, conscious and unconscious. I know that whenever I am feeling a particular emotion intensely, I tend to write poetry - this very well may be a form of sublimation for me.
The image attached to this post is a flow chart showing some of the different types of defense mechanisms, how they work, and examples.