The existence of two distinct types is actually a fact that has long been known: a fact that in one form or another has dawned upon the observer of human nature or shed light upon the brooding reflection of the thinker
— Carl Jung, Introduction to Psychological Types, page 11 (1923 English translation)

One of the great problems of history is that the concepts of and have usually been contrasted as opposites, polar opposites, so that love is identified with a resignation of power, and power with a denial of love Now we got to get this thing right. What is needed is a realization that power without love is reckless and abusive, and that love without power is sentimental and anemic.
— Martin Luther King Jr. Where Do We Go From Here?

"I don't think, Mr. Baker. I find out."
"Philosophers have only interpreted the world in certain ways; the point is to it". — Karl Marx, 11th Thesis on Feuerbach

"The philosopher should say to the activist something like the following. To change the world is not necessarily to improve it. To improve it is to make it better. For this two things are required. First, one must understand the world and the people in it both as to what they actually are and as to what they are capable of. In particular, one must possess a sound understanding of human nature. Second, one must know how things objectively ought to be. Can the various activists and world-improvers claim to know these two things? Well, they can claim to know them, but not with any show of legitimacy. Truly ameliorative praxis must be based on sound theory concerning what is and what ought to be, and this alone philosophy can provide — if anything can provide it I suggest we turn Marx on his head: The activists have variously tampered with the world, often with horrendous results; the point, however, is to it." — William F. Vallicella

What if both these guys are on to something?

The idea that not all individuals are constructed on the same ground plan — that there might be two human natures instead of one — has haunted philosophy since the Greeks. Indeed, what if there were three, or more, basic character types?

The literature of modern psychology is rife with amusing speculations in this area, but little that can be called serious. The classic exceptions are James and Jung, both covered in the timeline given below. You can also see an outline of Paul's basic semantics, a timeline of polarity awareness, and a selection of interesting quotations from historical sources, by clicking on the following links.