On the issue of theories in the scientific world. I suppose that there are two ways to attack a theory.
A. The first is the most basic. To show that it isn't true. For instance, a theory should, ideally, say something both substantive and true about the world. Perhaps the most common way of attacking a theory is to try to show that the theory fails on the 'true' part - that the theory is false.
B. To show that the theory is lacking it's "substantive" part. Thus, the theory is true, but it proves nothing. For exampe: Suppose that you go to bed early on election night, and the next morning want to know who won the election. Your roommate - helpful and insightful as usual - informs you that "The winner won." You aren't too impressed with your roommate's answer. But what is the problem? What your roommate has told you is indeed *true* - it is very nearly tautologically true. In fact, had your roommate named one of the candidates, there would be at least a chance of the answer being wrong. By saying "The winner won", your roommate has given you an answer you can be absolutely confident of - that answer *has* to be right. So the issue of *truth* isn't why you aren't terribly happy with that particular answer. The problem is that you haven't learned anything new, your roommate hasn't told you anything of _substance_. You didn't need your roommate's help to figure out that the winner won. Your roommate's answer is an empty truism.
Alright, so someone poses a theory. Say the theory is 7=6.
This theory can be disproven by the very nature that 7 does not equal 6.
Now, remember back in algebra when you had to solve X number of equations with X number of variables? And then we would get all excited when it looked like we were getting close to solving one of those variables, but when we got through all the number crunching, we got an equation that looked like this, 7=7. This equation by definition must be true. But unfortunately it does not help a bit. It tells us no useful information, so thus this theory is false.