(copied from costrin's thread)
Cognition divides into conscious - judging /unconscious - perceiving
Perceiving divides into sensing (instinct + sensory input + sensory representations) and intuition (ideas + analogies + metaphor + themes, etc.)
Judging divides into thinking (true/makes sense/works) or feeling (right/good/appropriate)
Then all functions divide into introversion and extroversion. Extroversion is the attitude that every piece of the environment is important and focusing too much on one thing is bad because of missed opportunities. Introversion is the attitude that things should be processed in depth, and that keeping track of each piece of the environment is bad because it takes too much processing power.
So the difference between Fe and Fi is that Fe keeps track of as many environmental variables as possible when making conscious value judgments (unconscious value judgments are in the realm of intuition), whereas Fi picks a select few environmental variables and thinks their moral consequences through in depth. Fe is "scared" of missing an environmental factor, and Fi is "scared" of not thinking through a conclusion deeply enough. (You guys can figure out Te/Ti from this.)
The difference between Ne and Ni is that Ne looks for all opportunities to make a new metaphor/idea, and Ni picks a few and tries to make as many ideas as possible. The difference between Se and Si is that Si filters down environmental factors in order to explore them in depth, whereas Se wants to keep all opportunities open at all times.
Yeah, I hope that made sense.