The leading function, also called the base, program, or simply first function, is an individual's most dominant psychic function. It describes in general terms the person's most comfortable thinking patterns, perspective on life, state of mind, and behavioral style as well as their positive motivational forces (what they pursue most vigorously when they have a choice). The leading function is critical to interpersonal dynamics because people constantly and inadvertently make judgments, assessments, and assumptions based on it. These comments and judgments portray a particular set of core values and share a common vector or general message, and those who the person interacts closely with must be accepting of this message for interaction to be cohesive and compatible.
Generally speaking, the leading function perceives, processes, and produces information most intensively. When a person "speaks" or "acts" from their leading function, they convey a sense of robust confidence and often begin to speak categorically, persuasively, and using exaggerations.
Proper development of one's leading function is generally seen as being crucial to personal development. This requires having people around you who are accepting of your core values and most natural, confident behavior styles. Profession-wise, the base function provides the best platform for developing a unique niche that will bring real value to other people. Rather than describing the professions a person would be best at, the base function describes a general approach and behavior style that can be successfully applied to virtually any field of activity.
Use of the base function comes effortlessly and produces a sense of internal satisfaction regardless of any external rewards. Base function activities can easily be developed into highly effective and productive skills, but there is also a tendency to indulge too much in the base function just because it is easy and rewarding. When overuse becomes extreme, a feeling of emptiness and pointlessness follows, and use of the base function stops bringing satisfaction.
The influence of the base function on perception and core values is so strong that people tend to project these values onto other people: everyone else surely must want the same things that your base function strives for. This projection is often a source of conflict with other people who have opposing values, but it is also one of the mechanisms for dualization. The base function's empathy towards others stimulates duals (and, to a certain degree, activators and semi-duals) to try to take care of the other person's problems with the corresponding function. This is exactly what the dual is looking for subconsciously, since one dual's base function is the other's suggestive function. However, in many other cases a person's natural interest in aspects of other people's lives that correspond to his own base function creates mistrust and strained relations.
According to the dimensionality of functions, the base function is able to effectively process and apply personal experience and social norms, present different solutions for different situations, and recognize and extrapolate the development of this aspect of information over time. The time dimension, which is shared by the demonstrative function, allows it to "fill in the blanks" between two related aspects, thus allowing it to infer the existence of previously unknown content.