Damn, I had this post at INTPc and I can't find it
Originally Posted by rivercrow
The main differences, theoretically, between Keirsey's vs MBTI is the structure behind each.
In MBTI, one observes, tests for four traits and assumes the heirarchy inherent in that type. In Keirsey's, the traits are treed - that is, there is an assumption of dominance of the four traits.
They run (effectively):
Unlike MBTI, the dominant traits in Keirsey's play a far more important role than the sub-traits, whereas in Jung/MBTI, E/I plays the dominant role (though MBTI expresses this as attitudes).
For example, in MBTI, INTP and ISTP are viewed very similary, while in Keirsey they would be miles apart because they divide at the top of the tree.
One major advantage to Keirsey is that it looks at behaviour only, which tends to be more pragmatic.
For all intents and purposes, you can easily translate MBTI types into Keirsey's types, just so long as you aren't doing research or something similar. If you want to apply the theory, however, you need to explain it to people differently - the two theories do not mesh well together at all, despite being based on very similar personality facets. In general, the easiest is to explain the NT/NF vs SJ/SP as that will cover 90% of Keirsey.
And of course, I highly recommend using FFM instead.