A few clarifications to prevent confusion...
cntrational wrote:
Scientists follow what's now called postpositivism. The modern formulation was created by a guy named Karl Popper, and thus it's often called "Popperian postpositivism", but it dates back to Newton, who phrased it such: hypotheses non fingo -- "I do not frame hypotheses", but less literally, "I do not engage in untestable speculation".
Newton's views were closer to empiricism than to Popperian critical rationalism.
Most formal logic you read about talks about evidence supporting theories, but in science, it's the other way around.
If it talks about evidence and theories, it's not formal logic. Formal logic talks about premises and valid deduction - it has nothing to do with evidence or theories.
Reality provides evidence
This is the fallacy of the myth of the given. Respectable people no longer believe this.
that we need to describe. We call these observations and phenomena.
It is important to distinguish between observations and phenomena. Phenomena are the things that are present in the world of sense and perception. Observations are more technical, but I guess we could loosely say that they're the kind of experiential events that are likely to have the potential to change our beliefs about phenomena. The point is, the phenomenon is what we're trying to explain, the observation is how we learn about the phenomenon.
What we call theories, scientific theories, describe the evidence.
No! A scientific theory
predicts observations. Reviews and descriptions of evidence are important in order to judge theories, and inspire new theories, but they are not themselves theories.
When a theory is disproved, it failed to describe the evidence accurately, and has to be replaced by a new theory.
We should probably note that a theory is never actually disproven - this is logically impossible! This is why the scientific method is required: the scientific method is NOT about disproof, it is about falsification. Which is a procedural system that does not guarantee truth, and which must be justified instrumentally. Essentially, it is a social contract in which scientists say "I will say I was wrong if..." and hem that "if" in with standard ethical rules and social norms and so on (which essentially amount to 'I won't be an arse about it' - since it's always rationally possible to deny that any falsification criteria have actually been met). This does not amount to disproving anything - it's just a promise to (for now) stop claiming that something is true.
This does not change the fact that evidence exists, and has to be accounted for.
That's a bit misleading. Both the nature of the evidence, and the scope of what is and is not evidence, is theory-dependent. There is no evidence until there is a theory...
All scientific knowldege must be testable, repeatable, and disprovable.
Falsifiable, not disprovable. And no, this is not the case (it's obviously impossible). You mean specifically
scientific theories, not all scientific knowledge (you can't have falsifiable theories unless you also include a whole bunch of axiomatic, untestable stuff as knowledge). Even then, 'repeatable' isn't exactly the issue - it's more 'non-non-repeatable' - because you can have valid scientific knowledge about, say, a supernova, even though those observations can never be repeated.
If there is no possible situation where your theory can be disproved, then your theory cannot be used for anything useful,
Well that's not true. "1+1=2" is a paradigm case of an unfalsifiable theory, but is useful. "If there is no possible situation where your theory can be falsified, then your theory cannot be used for anything useful" is another example of an unfalsifiable theory (in this case, an ethical theory! Since 'useful' is a term that only makes sense within a specified value system). "People shouldn't torture puppies" is also unfalsifiable. So are "that tastes delicious!", "I love you", and "I have a headache"...
and cannot be improved
That's not really true. Empirically, empirical theory did improve considerably even without explicit falsification criteria. Empirically, most modern science also does not use explicit falsification criteria, and while it's not perfect, it clearly involves improvement in some instances.
An accepted theory is thus just one that describes the universe accurately.
That's an unfalsifiable theory, and it's also false. Many theories were accepted, but did not describe the universe accurately.
Disproving a theory doesn't alter the universe, it just means our abstractions were wrong.
An unfalsifiable, essentially religious doctrine.
Note, however, that disproven theories are often retained as easier to use approximations. Newtonian physics is an approximation of Einstein's general relativity...which turned out it turn to be incompatible with quantum mechanic's Standard Model, which is conversely incompatible with general relativity. Not to mention that the SM says gravity dosen't exist, which is plainly not true. Searching for a theory to merge them is a goal of physics.
The SM doesn't say gravity doesn't exist. It just doesn't explain it. And 'approximation' is an unfalsifiable concept by definition.
Now, when I say that a scientific theory must be testable, I mean it. If it can be disproved, it must be done through evidence, not by pure reason, as Kant would call it.
On the contrary, reason is the only thing that can disprove something. As Kant points out in the Critique of Pure Reason, reason is the arbiter of truth in all judgements. And that can include pure reason without evidence. For instance, if I type in "1/0" on my calculator and it says "7", my evidence (good calculators have been shown to be extremely accurate when it comes to mathematics) and my reason (I can work out for myself that 1 divided by 0 cannot equal 7) conflict. It is my pure reason that tells me to ignore the evidence - or, more accurately, it is pure reason that tells me what the evidence is evidence of (in this case, that my calculator is faulty) and what it is not of (that on this one occasion, division of unity by zero was possible and yielded 7).
You can't learn about the universe simply by thinking really hard about it. (Ever hear of the book Critique of Pure Reason? The title might make more sense to you now.)
Consider:
a) either the scientific method yields more accurate knowledge of the world (than alternatives) or it does not.
b) if we knew that it did, we would know something about the world (it is a world in which scientific method yields... etc)
c) so if we knew a) through reason rather than through evidence, it would be possible to learn about the universe through reason rather than evidence
d) to know a) through evidence would require evidence about the accuracy of scientific knowledge vs the accuracy of non-scientific knowledge. This in turn requires knowing i) what science says is the case; ii) what non-science says is the case; and iii) what is in fact the case. We cannot supply iii) through science, as that would be begging the question, nor through non-science, as that would be begging the question. Therefore we cannot supply iii) through any method. Therefore there can be no evidence about the accuracy of scientific knowledge.
e) therefore either we know about the accuracy of the scientific method through reason, or we do not know about it at all
f) by c), if we know a) through reason then reason is enough to let us learn about the world. But if we do not know a) at all, then we cannot say that scientific methods are a better way of learning than reason is.
So either your claim is false, or else there is merely no reason (or evidence) to think it true.
So why do we do science? Well, in d) we cannot have direct evidence of the accuracy of science. But we can have evidence that people who follow science are less surprised by observations. If we then assume that a theory that renders the universe relatively unsurprising is an accurate theory, then we can justify science.
But that theory in turn requires us to believe that the universe actually is inherently a consistent, reliable, unsurprising place. And that is an axiom that, at most, can be supported by reason (if that!), and certainly not by evidence...
The adoption of Popperian-Newtonian science eventually caused Freud to become known for being a bunch of horseshit in psychology, and linguistics is increasingly in that vein as well. Many of, say, Chomsky's assumptions have been increasingly contradicted by reality, as have the derivative theories like universals, which turned out to be more "tendencies". Even things like ethics, considered the domain of philosophy, may be solved by the scientific application of game theory, evolution, and psychology.
I don't think you know what some of these words mean.
Now, here's a thing you have to know: most scientific research findings are wrong. Any value can vary by the testing set up, possible researcher bias, and by pure chance, and a piece of research may get an inaccurate result. Thus science must also be repeatable, a theory must be tested multiple times, to ensure that the observation was accurate.
Repetition of an experiment
does not ensure that the observation was accurate - that is the whole point of falsification vs verification.
Philosophers often disagree with Popperian/Newtonian philosophy, but to be frank, it produces results. We know of no other philosophy that allows us to accurately describe the world and gets us the information we want to do things, to describe the universe accurately. We might be wrong, but we don't seem to be wrong just yet.
This is all a religious dogma. And ignorant, too (philosophers rarely disagree with Popper that much (and Popper was a philosopher; this entire thread is philosophy)). And Newton didn't follow anything resembling critical rationalism. For instance, one of Newton's theories was that the planets didn't stop spinning
because the hand of God periodically added the required additional spin lost to friction with the aether. This is not a theory popper would have approved of, as there is no way to disprove divine intervention...
Politics, for example, won't work with this, but we can't replace it until we learn a lot more.
A strange exception. Political science does indeed attempt to follow the scientific method.
P.S. Critical rationalism is not in fact "the" scientific method, though it is often advertised as such.
Hope that cleared up a few points you were confused on!
EDIT: on learning about ethics through psychology: this is exactly the same as saying "we can learn about lava by analysing the psychology of people who use the term 'lava'" - rather than, say, analysing lava. Of course, you may believe there's no such thing as lava. But you cannot demonstrate "volcanos do not in fact errupt lava" purely by examining the psychology of people living near volcanos - you have to actually look at the volcano at some point! So in saying 'there is no lava, lava is a myth!', either you are fallaciously extrapolating from the psychology of those who believe in lava (which cannot tell you anything about the existence of lava itself), or you are making a claim based on the study of alleged lava phenomena themselves, in which case you are
not only studying psychology.
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Papuan languages, Morphophonology, Lexical Semantics 
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to Trailsend. Sal knows his stuff.