English 102

Assessing Reasoning: Evidence

There are different ways of assessing reasoning. I think the simplest is by looking at premises. Another is by looking at fallacies. And a third is by evaluating the evidence. Really evidence and reasoning are two aspects of the same process of thought. In this document I explain how you can use the evaluation of evidence as a way to assess the reasoning.

You may find this helpful, and you may not. If you don’t, ignore it.

Evaluating Evidence

In class we have discussed three points to look at when evaluating evidence—is it

Now, it turns out you can actually analyze most flaws in reasoning in these terms, too. Here are a few quick examples.

Take the flawed Socrates syllogism again (described in the page on Fallacies):

All men are mortal.
Socrates is mortal.
Therefore, Socrates is a man.

Well, what is the evidence here? It’s the premises: All men are mortal, and Socrates is mortal.

Is the evidence sufficient? I would say yes, in that the first premise tells us about all men, and in the second, we don’t need to know about other people, just Socrates.

Is it relevant? Aha—here’s a problem. The fact that all men are mortal turns out to be irrelevant to the question of whether Socrates is a man. It doesn’t help us. As we saw when we talked about fallacies, we really need a different premise: All mortals are men. That would be relevant, but it is false.

Take the special pleading fallacy: the company didn’t talk about the negative aspects of their product. What is their evidence? It’s all the good things they say about the product.

Is that evidence sufficient? In a sense, yes. There’s lots of evidence to prove that the product really does all these great things.

Is it relevant? Again, I would say yes. It all applies to the question. It’s all about the product and its features.

Is it representative? Uh oh. It doesn’t look representative. The “special pleading” charge basically accuses the company of cherry-picking their evidence, selecting only that which will support their case. If you disagree with an author, it may be because you feel that the evidence does not fairly or accurately represent the whole picture. It’s not representative.

I could go on, but I won’t. As I said, if this helps, great—use it. If not, skip it.

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Your Paper

This section refers to your Critique Paper. For the homework leading up to the paper I just want you to take notes on 2 or 3 points in the article and decide what you think of the reasoning. Is it valid? Are the premises reasonable?

If you use the evidence approach to evaluate the reasoning in your Critique Paper, you will need to distinguish this part of your paper from the part where you are focusing on evidence. In other words, you'll have one section that evaluates evidence in its own right, and another that uses evidence to evaluate reasoning. This means bringing out the process of thought, the relationship between premises and conclusions, in the reasoning section. Probably the best way to do this is to combine the concept of premises or assumptions with your analysis of the evidence. For example:

The article’s evidence about XYZ forms a key premise for the thesis. However, this evidence is not fully representative, because the author does not consider the evidence on the other side of the question, evidence that contradicts the thesis. Therefore, the conclusion does not follow.

You'll also need to use different examples in the two sections. Don't give the same examples of his evidence in the evidence section and in the reasoning section.

If you plan to use this approach, it would probably be a good idea to talk to me about it ahead of time.

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