Ad Hominem Attacks

I frequently come across logical fallacies while reading the newspaper, especially in editorials and letters to the editor.

But what, exactly, is a logical fallacy? It is basically a misapplication of logic. Logic, of course, is very important, as it helps us think through problems and hopefully reach valid conclusions. In fact, we use logical structures every day. For example, we often say such things as "If A is true then so must B." The classic if...then structure.

So, if A is true, does it follow that B is true? Well...not necessarily.

Let's take a look at a guest column in the State Journal-Register (Springfield, IL). This column, named "In My View," provides readers the opportunity to write extended essays on topics of the day. I have contributed essays to that column myself.

In the January 31 edition, a fellow named Steve Sullivan wrote a piece titled, "Economic Woes Tied to Dem Policies". The thesis is pretty clear, but he uses a particular logical fallacy called "argumentum ad hominem", also known as the personal attack. Wikipedia provides a good definition of the ad hominem: "consists of replying to an argument or factual claim by attacking or appealing to a characteristic or belief of the source making the argument or claim, rather than by addressing the substance of the argument or producing evidence against the claim."

Let us condider an example from that SJ-R column. Sullivan writes, "The biggest recipients of Fannie and Freddie largess from 1989 to 2008? Christopher Dodd, Obama and John Kerry. Obama has received four times more money from Fannie per year than any other senator in the last 20 years — $42,116. That’s 49 times more than John McCain."

This statement has nothing to do with Sullivan's thesis. It is, quite simply, an attack on two persons and does nothing to support the argument that democratic policies resulted in the "sub-prime" crisis.

So back to the top: If A is true, does it follow that B is also true? Let's see: Let the contributions to then-Senator Obama be 'A'. Let the sub-prime mess be 'B'. Clearly A is true, but since it does not address the question of democratic policies, it does not lead to B, it is a fallacy.

Logic? Who needs it.

"Logic? who needs that froo-froo, stuff anyway? It all just comes down to semantics." I have heard such sentiments from a variety of people. But the fact is that we all need logic and use it every day.

But let's start with the fact that we all use it. If you are reading this blog entry, you are using one of the great inventions enabled by logic: the digital computer. (Despite my youthful good looks, I am old enough to remember when there was a distinction between "digital" and "analog" computers.) Digital logic in use today is a result of the work of Augustus de Morgan, an English logician and mathematician from the nineteenth century.

De Morgan's rules go as follows:

not (P and Q) = (not P) or (not Q)

not (P or Q) = (not P) and (not Q)

These rules are applied by engineers in the integrated circuits and software in use in all modern computers. And cell phones. And TV's. And ....

More broadly, why do we need logic? We need it in order to sort out complex problems and, hopefully, formulate solutions.