Scientific truths are "objectively" true, i.e. true regardless of our preferences and the specific ideas that happen to be in our individual minds. We can further subdivide (or place on a continuum) scientific into general or universal truths, more or less "deep" principles that govern all or most social phenomena, and accidental or historical truths, all the millions of accidents of history that have become embedded in our social and political constructions. This subdivision closely corresponds to what we know about biological evolution: there are deep truths that govern all of biological evolution, and there are accidental truths about what variations did or did not arise, and which of those variations did or did not happen to survive selection pressures.
Preferential truths are precisely those preferences that do in fact exist in our individual minds. It appears to be a scientific truth that human beings primarily have preferences and act as best we can to fulfill those preferences. The specific preferences we actually have are themselves the result of scientific truths, general and accidental. (Strictly speaking, preferential truths are scientific truths: facts about the physical world with a causal history composed of general, universal and accidental truths. I single them out because they are especially important truths to human beings.)
While preferences and their distribution are facts, they are time-dependent facts: they change over time in the same sense that physical reality changes over time. It's a fact that my "bad kitty" coffee cup (right now) is empty and in the kitchen cabinet; it may be a fact (tomorrow) that it's full of coffee and on the desk in my office. Likewise preferences and their distribution can change over time: all the preferences that we have today almost certainly will not be all the preferences we have tomorrow.
Normative truths are truths about what preferences and social organizations we should have. As it turns out, there are no normative truths substantively distinct from either scientific truths or preferential truths.
For example: in a sense we "shouldn't" have the widespread desire to commit suicide before reproducing. But it's a scientific truth that such a desire (or the biological infrastructure that enables or promotes such a desire) cannot become prevalent: nature will inevitably select against this sort of desire. To the extent that we want to talk about normative truths as being substantively distinct from scientific truths, we could not call this truth specifically normative.*
*Of course, one might want to just call "normative" a synonym for "scientific". There's a valid (albeit silly) argument about the nature of God which says that God has actually actualized His own normative beliefs as the physical laws of the universe. If an extant omnipotent being really did have preferences, it would seem reasonable to conclude those preferences would be universal and immutable and our compliance ineluctable, precisely the character we observe of fundamental physical law. The idea that a God would have an actual preference and create a world where that preference could be frustrated or unfulfilled is arrant nonsense: a preference that one does not fulfill when it is possible to do so is no preference at all, and an omnipotent being cannot by definition actually have a preference it is logically impossible to fulfill.
If normative truths really were substantively distinct from scientific truths, we could not know any normative truth. We obviously cannot use the scientific method: scientific truths are precisely all and only those truths known by the scientific method; any normative truth we could know about the scientific method would be ipso facto not substantively distinct from a scientific truth. Furthermore, a scientific theory is known to be true only because observation never contradicts the the theory. Normative statements, however, are comparative: they compare what we do actually observe (or theories that scientifically proven true by observation) between "better" and "worse".
But "better" and "worse" are preferences. To be distinct from preferential truths (i.e. truths about the preferences we actually have) a normative truth must be true even if our preferences were globally contrary (i.e. every human being who has or will ever actually existed). Otherwise, it's a preferential truth or a scientific truth about the distribution of preferences.
Human beings are nothing but bundles of preferences (which are brute facts) and scientific beliefs, i.e. beliefs about the objective physical world (including self-referential scientific beliefs about our own and other people's preferences, their distribution and causal history) we use to fulfill those preferences.
I have come to the conclusion that almost all philosophy is bullshit because it appears that the overriding "mission" of philosophy is to establish normative truths as substantively distinct from scientific or preferential truths. As such it is doomed to creating nothing but ever more elaborate delusion, because there is no such thing as a normative truth. I say almost all because every now and then a philosopher comes along who learns how to think more effectively and efficiently; to do so they must first abandon the philosophical mission of establishing normative truths.
Almost all political philosophy, therefore, is bullshit. Anarchism, communism, socialism, capitalism, Libertarianism: all bullshit. These political philosophies all are about the preferences and social organizations we "should" have. Almost all philosophy (including and especially political philosophy) is the attempt to justify the philosopher's individual preferences as general or universal scientific truths. But there are only specific brute facts about what we presently want, the knowledge of reality about how world works, and the actions we take to change the physical world to get what we want. There are only the preferences we do actually have, and how we can cooperate or work independently to best fulfill those preferences.
What almost all philosophers do (especially political philosophers) is an inversion: Thus-and-such is what I prefer, scientific theories about the world that would make what I prefer predominant are therefore true. Most political philosophers justifying the existing social order (such as Aristotle) conclude that because their preferences are indeed predominant that the scientific theories about the world that would make those preferences always predominate must therefore be true. Most political philosophers criticizing the social order still believe the scientific theories are true that would make their preferences predominate; the reason that those preferences don't predominate is that most people are deeply deluded about the scientific truth and are acting irrationally.
(Of course, most people are indeed deeply deluded about scientific truth and do act irrationally, which tends to help the prima facie plausibility of every critical political philosophy. And of course no philosopher of any stripe would make his fallacy so transparent: skill in philosophy typically consists of obfuscating and concealing one's fallacious reasoning.)