Donald Rumsfeld once justified attacking Iraq without firm
evidence that his target possessed the ultimately apocryphal
"weapons of mass destruction" by citing fear of the
unknown:
Reports that say that something hasn't happened are always
interesting to me, because as we know, there are known knowns;
there are things we know we know. We also know there are known
unknowns; that is to say we know there are some things we do not
know. But there are also unknown unknowns − the ones we
don't know we don't know. And if one looks throughout the
history of our country and other free countries, it is the latter
category that tend to be the difficult ones.
That worked really well in Iraq. But it works even worse with
differential etiology, often referred to, not particularly
correctly, as "differential diagnosis." That's
because the "differential" part of this testimonial
technique is really just a form of circumstantial evidence –
a "process of elimination."
