PHL100: Reasoning

### Scientific Method

Where do we get theories from? There is no set method for creating philosophical theories or mathematical theories. There is one for creating scientific theories, however. This is called the Deductive Nomological Theory of Science, with Falsificationism. The underlying idea of the method is:
• We develop a hypothesis that there are certain natural laws or certain effects of natural laws. These hypotheses must be falsifiable: they must entail predictions which are in principle testable and could be false.
• We predict what (ideally unexpected) results such laws or effects will have.
• We check to see if these predictions come true; if they do, we know that hypothesis may be true and may continue to believe or use that hypothesis; if the predictions prove false, we reject the hypothesis.
• We continue to try to falsify the view.

A schematic example:
• Suppose H is a hypothesis. H entails predictions P1 ... Pn that are testable.
• We look to see whether P1 ... Pn occur.
• If these predicted phenomena are observed to be true, we continue to hold H as a hypothesis. (We especially are inclined to consider H likely if any of these consequences are unexpected.)
• If any of the predicted consequences is observed false, we reject the hypothesis.
The "deductive" part here is the inference from hypothesis to consequences. The "nomological" part is the the presumption that we are aiming to discover laws ("nomological" means reasoning about laws).

Some important corollaries of the deductive nomological theory with falsificationism
1. We cannot prove a scientific theory, we can only show it is better than any of the offered alternatives (by the criteria of the method and those listed below for comparing theories).
2. Science is creative: you must come up with hypotheses before you can apply scientific method.
3. A scientific theory (that is, a theory about the physical world, not a logical theory) which is not falsifiable is a bad theory!
Why does it matter that a scientific theory must be "falsifiable"?
• What kind of claim is not falsifiable? Examples include:
• All bachelors are unmarried males.
• 2+2=4
Most are inclined to believe that what distinguishes these examples is that they are true either in terms of meaning (analytic) or are consequences of other premises (logical claims).
• Unfalsifiable claims are thus usually presumptions, perhaps vacuous, that are dressed up like substantive claims. Typically even the person making the unfalsifiable claim is deceived by their own terminology and misses the ambiguity.
• Example: economists often claim all motivations are selfish. Confronted with the observation that some people appear to do altruistic things, they say these people desire to do altruistic things and so are selfish. But note: "selfish" on this kind of view means nothing more than something like, does what one wants to do. That is fine -- economists should be allowed to define any terminology they want -- but it is a different meaning than we usually use for "selfish." Furthermore, to say people are "selfish" on this view is not to make a claim -- it is to state an assumption that they make in all their reasoning!

Choosing between theories
The Deductive Nomological Method with Falsificationism does not guarantee that we will have only one theory. (We use "theory" to mean at least a collection of one or more hypotheses.) There may be very many different and contradictory hypotheses that pass the method as explanations of some one phenomenon. To choose between theories, we use three ranked criteria:
1. Predictive power
2. Consistency with existing scientific theory
3. Simplicity

The Duhem Thesis
Pierre Duhem recognized that sometimes we discover things that are inconsistent with our hypotheses but we are inclined to keep our hypotheses. This is because, he realized, we never really test a single hypothesis, but rather a number of them as a group. We assume also, for example, that our measurement instruments are working well, that we have not made a mistake in our mathematics, and so on. But it then follows that when a prediction is made, and then found false, and one of these other assumptions could be false.

A more sophisticated version of the deductive nomological method with falsificationism thus looks something like this:
• Suppose H1 is our new hypothesis. H1 and a range of additional hypotheses H2, H3, H4... Hn entail predictions P1 ... Pn that are testable.
• We look to see whether P1 ... Pn occur.
• If these predicted phenomena are observed to be true, we continue to hold H1 as a hypothesis. (We especially are inclined to consider H1 likely if any of these consequences are unexpected.)
• If any of the predicted consequences is observed false, we reject the one or more of H1... Hn.