T's rationalize first, feel second.
F's feel first, think rationally second.
Simple as that.
I must also add; T and F have nothing to do with "intelligence" as it is defined by the dictionary. T and F have their strengths in different areas, but a truly intelligent, well developed person will be adept at both. We need both to survive and adapt. So don't hold the fact that someone is T or F dominant against them.
For Example: An NT can theorize all day long, analyze complicated systems, but if they cannot apply this to the real world or hold a decent enough conversation to make something out of himself; how intelligent is he really?