Modus Ponens versus
Likely the most commonly witnessed failure of logic when debating the intransigent political fanatic or the fundamentalist religious extremist is known as affirming the consequent. Unless put into perspective this fallacy is a bit difficult to comprehend, but once defined the logical failure becomes evident.
Affirming the consequent is categorical in nature and essentially relies on reversing the argument to make available evidence fit or confirm a bias. A recent example is the contorted ballyhoo that followed the Department of Defense announcement that vintage chemical weapons had been unearthed in Iraq. The right wing machine went into full tilt boogie proclaiming that the Bush/Cheney justifications for invading that country had been vindicated. This in spite of the DoD stating in the very same report that the shells were completely useless and had been for decades.
The premise in such an argument is actually valid, yet there is a glaring error between the premise and conclusion. The motive of the right-wingers is to foment the false assumption that the premise (Saddam had WMDs) is actually the conclusion. In truth, the premise is only one of several conditions required to prove the conclusion. Let’s look at it from a child’s eyes so that even the most biased, bigoted extremist might be able to understand.
To state that ducks are birds and that ducks swim in the water is the primary premise. The secondary premise would be to state that chickens are birds. The false conclusion would come by stating that since both ducks and chickens are birds, and ducks swim in the water, that chickens also swim in the water. Of course we know this to be incorrect because experience tells us that swimming is neither necessary nor a sufficient condition to define a bird.
We call this “getting the cart before the horse”, and it seems to be the ultimate in confirmation bias… a last port in the storm for the bigoted.
Let’s take this to politics.
Obama nationalized health care by passing the Affordable Care Act. The Nazis had nationalized health care. Therefore Obama is just like Hitler. It is difficult to understand how so many Americans cannot understand that nationalized health care is insufficient evidence to define Nazism. This is especially true since every country that fought against the Nazis now has nationalized health care, with the exception of the U.S.
Now let’s consider religion, specifically creationism.
Because of the backlash by rational, scientific thinkers, the fundamentalists prefer to call it Intelligent Design. In what has become known as the watchmaker analogy, the creationist tries to prove that just as a watch could not accidentally come to exist, so neither could a human being. Every creationist argument will find roots in the watchmaker argument.
Probably the best known of these arguments comes from Michael Behe, who calls it “Irreducible Complexity.” In his book, Darwin’s Black Box, Behe posits that certain systems are so complex that they cannot be explained by the accidental nature of evolution. He uses a mousetrap as his example. Ken Ham is fond of using a banana. Bill O'Reilly rather bizarrely uses the tides.
The premise is that a mousetrap (banana, the tides) was created… that it is the product of intelligent design… that it is an irreducibly complex object composed of several parts, all of which contribute to the function. The universe, and particularly humans, are also composed of several parts and almost unimaginably complex… therefore an intelligent designer must be involved.
By now you have figured out how to decipher attempts to affirm the consequent, so I suspect you can finish the story.