what is the most important branch of philosophy? This implies other questions that go into this answer. They are:

I use "How come" instead of "why" to refer to the superordinate principle in a non-teleological way. "Why" implies a motivation and a desired end state, "how come" refers to an end state with no conscious direction or cause. By "branch" I mean Metaphysics, Epistemology, Ethics, etc, as in "Randism in One Afternoon".

Is there a "most important" Branch? Well, philosophy is a tool, The usefulness of this tool is based on philosophy as a branch of knowledge. A good tool has some adjustability like a wrench, pliers, drill or microscope

How come there would be such a thing? There must be some part of this tool that makes it work.

To answer the last two questions in a way that makes sense, I will do them in the reverse order of which they were asked.

There are five branches of philosophy; Metaphysics, Epistemology, Ethics, Politics and Esthetics. If you recall from the discussion of philosophy I mentioned that certain things were irreducible primaries, that is, to analyze or break them down further you must go outside the realm of philosphy, while the rest are derived.

To be important, a branch of philosophy must be an irreducible primary. not further analyzable in philosophical terms. This is because it would need to be a basic topic of philosphy. For this we have two. Metaphysics (the way the world works) and Epistemology (the way we work). To figure out how best to govern ourselves (Politics) we must have some handle on good and evil. to get this handle (Ethics), we need to know what is to be expected in the way of behavior under what circumstances and what is possible. To project this in a sensory way (Esthetics) we must know what means a comprehensible world and "competent to" and "worthy of" living.

Metaphysics is derived from the "Special Sciences (Physics, Chemistry, Biology...)" but is a "super science" summing over the results of the others and identifying the common thread. Epistemology rests on the specific identity of Man. In the case of Randian Epistemology. "volitional rational consciousness" This comes from the metaphysical definition of Man. It becomes a separate branch because of some other quality. The specific psychological workings of the species at the top of the food chain on the third rock from the Sun.

Along with being a basic branch (Metaphysics and Epistemology), the most important branch of philosophy must be variable; having more than one setting. If it were fixed then I could not change those settings so that I could do nothing with it. This varaibility must be controllable; respond in a predictable way to what is done or applied to the settings. If either of these is absent then what's the point?

Metaphysics is fixed, that is, the topics are what are called "necessary" and these kinds of things follow one from the other inescapably and unalterably. If you look at Randite Epistemology, or any philosophical system's Epistemology. There is, stated or implied, a best way or "road" to understanding, usually one of 3 Reason, faith, feeling.

Some of these are mutually exclusive and one can choose amongst them, selecting different ones at different times or always preferring one over or at the expense of the others. So we know that Epistemology has at least 3 variable positions and that, in the adult human they are willfully selectable, later to become a habitual way of "doing business". And you can tell which a person has chosen. A feelings-driven mentality is in a constant state of flux and chaos, a faith/revelation based mind is in a constant state of doubt and a reason-propelled mentality is both steady and agile, and free of the angst that torment the other two (and, in a confrontation with either, able to exploit the disunity and the accompanying states of self-abnegation and torment to its own advantage to win: Just as a self-contained guided misslie is able to "lock on" to an enemy aircraft by detecting it's exhaust heat or radar "signature" and "homing in" for the kill).

Since to be the most important branch of philosophy, the branch must be both an irreducible primary and willfully variable, and since the only branch that meets both those standards is Epistemology, then it follows that Epistemology is the most important branch of philosophy. OK; so what? Well I can use this to enhance my mental function and I can also use it to analyze a philosophical system or question. for example, let's say there is a proposed law that rests on redistribution of wealth. Well, this rests on statism, which rests on the ethics of altruism which is the opposite of egoism. Now I know that Egoism is compatible with Objective Metaphysics and Rational Epistemology. Since Altruism (as coined and defined by Auguste Compte) is the opposite of Egoism, and since the opposite of A is not-A then I know that Altruism is incompatible with Reason and Reality. So, once I find that the proposed law is based upon redistribution of wealth, then I know it is evil and a disaster in the making: And it usually takes only a couple of seconds, too.

How is this applicable in real life. the Iraq War: I knew from history that the peoples were not compatible at this time with "self-governace" (a political system based on the primacy of individual rights) having been at each others' throats for 5 millenia. Beyond that, we might as well be Martians as far as they are concerened. Also there is no language where the words "friend" and "invader" are not on opposite sides of the "to be destroyed" divide, and, withthe exception of Sufi, "friend" and "infidel". Can you really compel persons to be free? I further knew that Hussein did not posess the weapons that he was alledged to by the Bush Administration, nor the wherewithal to use them meaningfully against the US, nor, being a secularist, was he suicidal, willing to launch a futile war "for Allah". Even Bill O'Reilley said on 11, March '03 "...There are no facts in play" (meaning that, in fact , the hypothesis was false) and the other radio rangers (read Kool Aid drinkers) were bemoaning the lack of real data from the Administration (and were therefore acting on faith or feelingss and not reason), I further knew that the United states posessed the tools to verify and had claimed in the UN to have the goods on the Hussein Regime quite emphatically and with enough certitude to claim a causus belli meaning a clear and present danger. So I know that claim was an outright, bald-faced, flaming lie. So I knew the war, and all it's consequences would be evil and a disaster because it would be imcompatible with reality and reason. If the Republicans continue to support this mess a landslide defeat is the least they deserve

Now, how did I know all this beyond the particulars of the situation? As a Randite, I hold that Reason is the sole tool of knowledge and works according to the process and rules of logic. to integrate the material provided to it (the particulars) in a non-contradictory, systematic, organized, hierarchical whole. In so doing, I have made it a mental habit to behave (think) in this fashion. So, I took the whole mess, put it in the frying pan, lit the gas and stirred it up and that's what I got.

Was I right? Well when the "Weapons of Mass Destruction" mantra went bust, the mission changed to "bringing democracy to Iraq [Republicans? Democracy? freedom in a land that would be a theocracy but for the Ba'athists? That's a laugh]" Now the mission is "the global war on Terror [after creating the conditions for Iraq to fall into the hands of Iran and Al Qaeda. that's a laugh]". What will it be Tomorrow? I know. "Pizza to the People [Cheese? Sausage? Papperonie? in an islamo-fascist state? that's a laugh]". The other mantra "Regime change" was neither a legitimate cause for attack nor any less airy-fairy than the Easter Bunny, so it was always a floating abstraction connected to nothing in reality: Pure, unadulterated B.S used as a catch-all when the "real" stuff s**t the bed, like Chronic Fatigue Syndrome, Irritable Bowel syndrome or the other Mass Sociogenic Disorders; for those of you in Washington DC. But anywho, it was a superior epistemology that gave me the tools this out. I report, you decide.

Here and elsewhere you have seen me use the following "...throw the whole mess in the frying pan, light the gas, stir it up and see what we get". the cooking analogy is exact. I put the material to be worked with (the whole mess) in one frame of reference (frying pan), light the gas (begin the process) stir it up (break down and re-assamble the concepts just as cooking breaks down the cell structure and releases juices and fats and they all moosh together) and see what we get. (the non-contradictory, systematic hierarchical whole)

That is why Epistemology is the most important branch of Philosophy. It is the link between the mentality and the outside world if it is the proper one and if it is not, it is just another form of being self-absorbed