Remember from Type Dynamics that each of one of us either extraverts our Judging (T or F) function or our Perceiving (S or N) function—and we introvert the other of these functions. The last letter of your Type (J or P) indicates which function you extravert. This is therefore the function the
Why use Temperament over Type?
OKA Intro to Judging-Perceiving
OKA's Hile Rutledge introduces the Judging-Perceiving dichotomy from the Myers-Briggs® model in his usual clear, compelling, informative way.