A while back I wrote a couple posts about the danger of overstating a conclusion and the importance of recognizing alternative explanations for evidence. I also blogged about the way in which science and scripture are interpreted (Nature vs. Scripture). Those posts each stand on their own; however, in this post I want to bring some of those concepts together and provide specific examples found in discussions between evolutionists and intelligent design proponents of overstating conclusions. Familiarity with the content of those posts will help you understand the content here.
We are going to look at two sets of arguments provided by each side regarding the similar body plans of humans and the great apes. We will look at why the conclusions are valid, thus exposing the limits of the conclusions. When we know the limits of the conclusions, we are less likely to overstate our case.
Common Descent Compatibility
Let's look first at an argument on the evolutionary side:
1. Humans and the great apes have similar body plans
2. Common decent has the ability to explain similar body plans
3. Therefore common decent has the ability to explain the fact that human and the great apes have similar body plans
As you can see this first argument begins with the premise that humans and the great apes do share similar body plans. This is the raw data of nature- the observation that is not disputed. In order to come to an interpretation (science), a second premise is required. The second premise comes from the theory of evolution, and it must include a mechanism that has the ability to explain the existence of similar body plans. Common descent is the mechanism in this case. Notice that I used the phrase "has the ability to". This is used instead of "does" in order to avoid begging the question (assuming the conclusion in one of the premises).
Using those two, we get the conclusion that common decent has the ability to explain the similar body plans of humans and the great apes. However, due to the fact that I only used the phrase "has the ability to" in the second premise, that is all that is logically permissible in the conclusion. This first argument merely establishes compatibility of common decent (premise 2) with the observation of nature (premise 1). It does not establish certainty that it does, in fact, explain it. We will return to this later.
Now, let's look at an alternative explanation to evolution. It uses a similar argument in support of intelligent design:
Intelligent Design Compatibility
1. Humans and the great apes have similar body plans
2. Common design has the ability to explain similar body plans
3. Therefore, common design has the ability to explain the fact that humans and the great apes have similar body plans
As with the argument on the evolutionary side, the first premise states the observation from nature that is not under dispute but needs an explanation. In order to come to an interpretation, we must have a lens through which to interpret the data of premise 1. The second premise provides this in this second argument. Since we are looking through the lens of intelligent design, we must look within the theory for a mechanism that can explain common body plans in nature. That mechanism is a common designer (no sense in reinventing the wheel- especially if you were the inventor). Once again, I have limited the second premise with the phrase "has the ability to" for the same reason as I limited the second premise of the argument on the evolutionary side.
The conclusion combines the first and second premises to come up with the deduction that common design has the ability to explain the similar body plans of humans and the great apes. Again, because of the limitation I placed on the second premise, this merely establishes compatibility with the theory of intelligent design, not certainty that it is, in fact, the correct interpretation.
Recognizing The Soundness of The Other's Argument
This is where people on both sides get into trouble. Notice that I did not only present one argument for compatibility. I provided arguments for compatibility on both sides. However, there are those who do not wish to recognize that the other argument is sound. Let's look at both arguments, then we'll analyze:
From Evolutionary Perspective
1. Common decent has the ability to explain the fact that human and the great apes have similar body plans
2. No other hypothesis has the ability to explain human and the great ape similar body plans
3. Therefore, common decent is the only idea that can explain human and the great ape similar body plans
From Intelligent Design Perspective
1. Common design can explain the fact that humans and the great apes have similar body plans
2. No other idea that can explain human and the great ape similar body plans
3. Therefore, common design is the only idea that can explain human and the great ape similar body plans
The first premise in each of these arguments is the same as the conclusion from the previous arguments from the respective perspectives. The second premise is required to get to the conclusion that is desired, but where both sides get into trouble. In order for a conclusion to logically follow from the premises (soundness), each of the premises must be true. The second premise in both of these arguments is false. That is evidenced by the very soundness of the competing argument discussed above.
How People Accomplish Overstating Their Case
This is where people overstate their conclusion (and case). They assert that their perspective is the only perspective that has the ability to explain a certain piece of data. The reason that I chose this particular observation from nature for the example is because this is an observation that it is easy to establish that both sides are able to explain. In the cases of many other observations of nature, one side will claim exclusive ability to explain the observation. If the similarity of body plans between humans and the great apes was one of these, it would be the second premise in the competing argument that would be disputed.
However, like the observation that I chose, there is much that the different views have the ability to explain. The problem comes when those supporting competing views refuse to recognize the compatibility. Of course, I'm not discouraging the peer review process (that is what these disputes result in), because that helps us refine our views by discovering inconsistencies (see "Importance of Consistency" and "Consistency Among Disciplines". However, there does come a time in which challenge after challenge falsifies a worldview or theory or observation after observation confirms a worldview or theory. We must be willing to act appropriately and not be so emotionally tied to the truth or falsehood of an idea that we do not accept or reject it for logical reasons.
How to Avoid Overstating Your Case
We must be intellectually and logically honest about evidence as it is presented. If it is compatible with a competing view, so what? If our view is, in fact, the correct view, it will also be compatible- that doesn't mean that we won't have to make adjustments- that is part of doing science and theology. If we are truly seeking truth, we will be willing to adjust when a particular view is constantly being falsified.
Also, there is nothing lost by granting compatibility of evidence with another view, except an unsound argument for the conclusion that our view exclusively explains reality. Most of the time, others know that that argument is unsound, so they immediately reject it when presented with it anyway, so why bother keeping it around? Good riddance to unsound arguments!
We must be careful that when we present arguments that we use appropriate qualifying words and phrases. We don't want to get caught with an invalid argument. We also must be willing to accept critique of our premises and be willing to defend or adjust as necessary. We don't want to get caught with an unsound argument.