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:

A schematic example:
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"?
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: