Denying the Consequence

I was discussing in class the other day about how scientists now disprove things rather then trying to prove something. I was pulling up information in my logic class the other day and I came across exactly what I was talking about. Let me see if I can explain what I meant a little better.

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There are two types of logical reasoning. One is deductive, and the second is inductive. Deductive logic has at least four forms. The one I was referring to in class is called Denying the Consequence. This writes out as

P implies Q                                                  when it rains, the grass gets wet
there is not Q                                               the grass isn't wet
therefore, there is not P                                therefore, it did not rain

Now, that is a valid argument form for deductive logic. However, a common fallacy in deductive logic is called Affirming the Consequence. This writes out as

P implies Q                                                when it rains, the grass gets wet
there is Q                                                   the grass is wet
therefore, there is P.                                   therefore, it rained

The second is a fallacy because there might be other factors that can get the grass wet, such as sprinklers or dog pee.

HOWEVER

In Inductive Logic (inductive logic is where you can state percents of something - example : x% of R observed are Z), Affirming the Consequence IS a valid argument form, and is sometimes used in science. It has another name though. We call it Induction by Confirmation.

If P implies Q                                                       P= some hypothesis Q = observation
we find Q                                                            Q = confirming instances
we can conclude, probably P                                P = conclusion

For example, I have a hypothesis that rain makes grass grow. P being rain, Q being grass is growing. X number of confirming instances I can observe that, when it rains and then the grass grows. We can conclude that rain probably makes the grass grow. With inductive logic there is no 100% yes answer. We can just conclude with X-confidence that this happens. Inductive logic coincides with evolution and Einstein's theory of relativity.

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Now, back to what I was saying before. In class I said that scientists more often then not want to Deny the Consequence because they are less tempted to change the results. This is because proving that there is not Q only has to happen ONCE before there is NOT P. With inductive logic, you can have X-many of confirming instances, and the amount of confirming instances you have determines how good your relationship is. And as we read in 'Mismeasure of Man' it was very easy to increase the number of 'confirming instances'.