You know, I think this holds true for BAs as well.
I'm getting a BA in international affairs and another in history. And quite frankly, I know shit about either subject. I can bs my way through, but I don't really know it. Not that they don't teach you anything, but come on. One class on the american revolution? One class on political geography?
It's not until grad school that you really start to know something about the subject you are trying to master. And then, even after grad school and that shiny new diploma, I suspect it takes years of actually working in the field to become truly knowledgeable.
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