"Understanding and Applying Jung's Cognitive Processes", she differentiates between the functions:Couple that with the Te-Se confusion at the auxillary level:Ni and Ti are often accompanied by a sense of detachment and disconniction. With both there tends to be comfort with complexity. The difference is what when we are engaging in Ti, we usually have a clear sense of the principles or models something is judged against, whereas Ni an impressionistic image forms in the mindcould confuse ISTPs and INTJs.Se and Te are often used when there is a focus on facts and empirical approach. Keep in mind that Se is a perceptive process and may consist of data gathering with questions, whereas Te is a judging process in which the purpose of questions is to establish logic.
Where the ISTJ and INTJ may become confused is at the dominant level where Berens saysSince they all are "Chart the Course" types (including INFJ), it is quite easy to make the confusion.Si and Ni are both more focused and involve perception of "one thing at a time". This gives the behavior a sequential appearance, with a sense of beginning, middle, and end. With Si, the sequenceis often logisitical in nature and based on the past, Ni is based on a vision for the future, and the focus is on what steps to take next.