Lords of Brain

This is a philosophical perspective to logical argument concerning the premise, evidence, and conclusion.

In logical argument a premise must exist.  A premise can be expressed as: “If A, then B.”  The premise expresses the logical relationship between the theory (A) and the assumption (B).  The philosopher is not concerned with the cause and effect so much as the logical chain of events between theory and assumption.  We call this logical chain of events, conditions.

The two primary conditions that exist in philosophical argument are necessary conditions and sufficient conditions.  Let’s explore the differences between the two.

If the assumption relies on the theory, then the theory is a necessary condition.  In other words, if A must exist in order for B to exist, then A is a necessary condition.  For example:  If I have an orange, I must peel it before I can eat it.  Therefore, peeling the orange is a necessary condition for me to eat the orange.  However, just because you have a necessary condition, it does not follow that B must occur.  I have peeled the orange and supplied the necessary condition, but I do not have to eat the orange.

This takes us nicely into the sufficient condition.  If the assumption (B) must follow the theory (A), then A is said to be a sufficient condition.  For example:  If I strike a match, then (given the presence of oxygen) the match will burn.  We can see that striking the match is a sufficient condition.

It follows that a sufficient condition is also a necessary condition; however, necessary conditions (by themselves) are not sufficient conditions.

We have now established the elements of a premise.   We can now use this premise to offer evidence in support of a conclusion.  It is important that evidence given must be independent from and supportive of the conclusion.

Suppose one wants to argue in favor of capital punishment.  One could construct the premise, “If a person is convicted of murder, he should be executed.”  Evidence could be given as:  “Capital punishment would prevent future murders from the convicted criminal, and is an effective deterrent against would-be criminals.”  At this point, we are not as concerned with the validity of that claim as we are with it being independent from and supportive of the conclusion (in the case, the enactment of the death penalty).  In this argument, we have established premise, evidence and conclusion.

The evidence is independent from the conclusion; which is to say, the conclusion does not have to exist for the evidence to be true.  It would be quite another thing if we offered the evidence to be, “Executions are a deterrent because we have capital punishment laws.”

The evidence also supports the conclusion.  If we can accept the evidence as truth, then it would follow that we could accept the conclusion as truth.

Now, we can begin to look at some common logical fallacies in argument.

Circular argument:  A circular argument presents evidence that is not independent of the conclusion.  “Capital punishment should be required of all murderers because they should be executed.”  In this case the evidence is essentially the same as the conclusion, and there is no independence.

Consider the following, “Carl is telling the truth because James says he is, and James believes him because Carl told him the truth.”  The conclusion, “Carl is telling the truth,” depends on the evidence, “James says he is.”  The problem is that the evidence relies on a second premise, the conclusion of which requires Carl to be telling the truth, which is the original conclusion.  Again, the conclusion depends on itself and is a circular argument.

Begging the question:  When evidence is presented in support of a conclusion that rules out any other possibility, it is said to be begging the question.  Carl could make the claim, “all Americans believe in capital punishment.”  Wayne could present the argument that James, an American, does not support capital punishment.  Carl might claim, “Then James is clearly not an American.”  Carl has redefined “American” so that his original conclusion is true, and has committed the fallacy of begging the question.

Non Sequitur:  From the Latin, “does not follow,” the non sequitur is used to describe a premise whose evidence (while being independent from) does not support its conclusion.

Sometimes evidence does not support the conclusion because there is no relation between the two:  “Carl is telling the truth because he is a democrat.”  Being a democrat offers no relation to Carl’s honesty (despite what a republican may claim) and cannot be used to support that conclusion.

In other non sequiturs, the evidence may support the conclusion, but only secondarily or, in actuality, supports a slightly different conclusion.  “Lowering taxes would be beneficial to Americans because it would allow them to keep more of their income.”  The evidence would seem to support the conclusion (of lowering taxes); however, it makes no statement of other social concerns, which may arise as a result of lowering taxes (fewer prisons, lower wages in public schools, reduced maintenance on public roads, etc.).

Any time a sufficient condition is required for the evidence to support a conclusion, a non sequitur occurs when only a necessary condition is given.

Look for Part 2 (coming soon) in which we explore even more logical fallacies of argument.