The Dynamics of Psychological Type
After publishing his seminal work on psychological types in 1921, Jung did little further work in this area. However the importance of his work was recognised by the mother and daughter team, Elizabeth Myers and Catherine Briggs. Realising that if Jung's ideas were to have any practical application it would be necessary to develop an easy method for assessing a person's psychological type, Myers and Briggs published the first type indicator in 1949. Moreover, they developed the now famous four-letter type code as a short hand way of describing a person's type.In addition to providing a short-cut route for describing a person's psychological type, the four-letter code also reveals a set of complex personality dynamics which provide insights into the order in which the preferred psychological processes are likely to manifest themselves in the person's daily life.
The way to discover the dynamic relationship between these psychological processes is by examining the middle two preferences; SN for perceiving, and TF for judging, types. These are referred to as functions. For any type, one of these functions is dominant and this dominant function is used in the preferred world (external or internal as indicated by the EI preference), with Extraverts using their dominant function in the external world and Introverts using their dominant function in the internal world. Moreover, the function which the type code indicates is not preferred is called the auxiliary function. Thus, if either the S or N function were indicated as being the preferred function, then either the T or F function would be the auxiliary function.
So, introverts are more likely to exhibit their auxiliary function when relating to the outer world, whereas their dominant function will be used mainly when relating to the inner world, and will thus not be readily accessible for others to see. In contrast, because Extraverts use their dominant function in the outer world, it will be available for all to see.