Key ideas of TA

Some core models and concepts are part of TA as follows:
The Ego-State (or Parent-Adult-Child, PAC) model
At any given time, a person experiences and manifests their personality through a mixture of behaviours, thoughts and feelings. Typically, according to TA, there are three ego-states that people consistently use:
Parent ("exteropsyche"): a state in which people behave, feel, and think in response to an unconscious mimicking of how their parents (or other parental figures) acted, or how they interpreted their parent's actions. For example, a person may shout at someone out of frustration because they learned from an influential figure in childhood the lesson that this seemed to be a way of relating that worked.
Adult ("neopsyche"): a state of the ego which is most like a computer processing information and making predictions absent of major emotions that cloud its operation. Learning to strengthen the Adult is a goal of TA. While a person is in the Adult ego state, he/she is directed towards an objective appraisal of reality.
Child ("archaeopsyche"): a state in which people behave, feel and think similarly to how they did in childhood. For example, a person who receives a poor evaluation at work may respond by looking at the floor, and crying or pouting, as they used to when scolded as a child. Conversely, a person who receives a good evaluation may respond with a broad smile and a joyful gesture of thanks. The Child is the source of emotions, creation, recreation, spontaneity and intimacy.
Berne differentiated his Parent, Adult, and Child ego states from actual adults, parents, and children, by using capital letters when describing them. These ego-states may or may not represent the relationships that they act out. For example, in the workplace, an adult supervisor may take on the Parent role, and scold an adult employee as though they were a Child. Or a child, using their Parent ego-state, could scold their actual parent as though the parent were a Child.
Within each of these ego states are subdivisions. Thus Parental figures are often either nurturing (permission-giving, security-giving) or criticizing (comparing to family traditions and ideals in generally negative ways); Childhood behaviours are either natural (free) or adapted to others. These subdivision categorize individuals' patterns of behaviour, feelings, and ways of thinking, that can be functional (beneficial or positive) or dysfunctional/counterproductive (negative).
Berne states that there are four types of diagnosis of ego states. They are the behavioural diagnosis, social diagnosis, historical diagnosis and the phenomenological diagnosis of ego states. For a complete diagnosis one needs to complete all four types. It has been subsequently demonstrated that there is in fact a fifth way of diagnosis. It is known as the contextual diagnosis of ego states. For example if a man says, “On July 5th, 2007 the alignment of the planets will create a magnetic field so large that there will be the biggest tides in half a century”, what ego state would be diagnosed?
If that man was of a dishevelled appearance, had not shaven for 2 days and was sitting on a park bench drinking out of a bottle in a brown paper bag what ego state would be diagnosed?. Probably some kind of regressed Child ego state. If that man was in an observatory wearing a white coat and carrying a clip board what ego state would be diagnosed? Probably Adult ego state. The different contexts for the same statement would tend to result in a different diagnosis. The context in which the statement is made is central to the diagnosis of ego states.
Ego-states do not correspond directly to Sigmund Freud's Ego, Superego and Id, although there are obvious parallels: ie, Superego:Ego:Id::Parent:Adult:Child. Ego states are consistent for each person and are argued by TA practitioners as more readily observable than the pats in Freud's hypothetical model. In other words, the particular ego state that a given person is communicating from is determinable by external observation and experience.
There is no "universal" ego-state; each state is individually and visibly manifested for each person. For example, each Child ego state is unique to the childhood experiences, mentality, intellect, and family of each individual; it is not a generalised childlike state.
Ego states can become contaminated, for example, when a person mistakes Parental rules and slogans, for here-and-now Adult reality, and when beliefs are taken as facts. Or when a person "knows" that everyone is laughing at them because "they always laughed". This would be an example of a childhood contamination, insofar as here-and-now reality is being overlaid with memories of previous historic incidents in childhood.
Although TA theory claims that Ego states do not correspond directly to thinking, feeling, and judging, as these processes are present in every ego state, this claim is self-contradictory to the claim that the Adult is like a computer processing information, therefore not feeling unless it is contaminated by the Child.
Berne suspected that Parent, Adult, and Child ego states might be tied to specific areas of the human brain; an idea that has not been proved.
The three ego state model has been questioned by a TA group in Australia, who have devised a "two ego-state model" as a means of solving perceived theoretical problems:
"The two ego-state model says that there is a Child ego-state and a Parent ego-state, placing the Adult ego-state with the Parent ego-state. [...] How we learn to speak, add up and learn how to think is all just copied from our teachers. Just as our morals and values are copied from our parents. There is no absolute truth where facts exist out side a person’s own belief system. Berne mistakenly concluded that there was and thus mistakenly put the Adult ego-state as separate from the Parent ego-state."