Failure in the Deductive-Nomological Method

As we have discussed previously on the philosophy of science, scientific reasoning employs a mixture of induction and deduction. More properly:

- A good portion of scientific explanation follows a deductive (deductive-nomological) structure.
- This deductive framework is characterized, in the case of experimental science, by general premises which are arrived at via induction (or abduction).

The second point is where pure logical deduction and scientific deduction differ - a distinction which frequently lies at the root of a misunderstanding and miseducation about the imperative veracity of scientific knowledge.

For example, this constitutes a true, pure logic deduction:

- Let all numbers greater than zero be positive.
- Object "a" is a number greater than zero.
- Therefore object "a" is positive.

Here, the general premise is logically undeniable (actually it's a bare definition - but it serves the point: nobody in their right mind would claim that a number greater than zero could be negative - the premise is axiomatically true). The following line then demonstrates that our specific object is a subset of some general rule/class. Because of this, the conclusion is inevitable.

A scientific, deductive-nomological argument follows a similar structure - only the general premise is a physical law (or model, arrived at inductive/abductively), and the lines following it are built to demonstrate that the specific physical phenomenon is a subset of the class of phenomena described by that general law. For instance, we explain why Susie's ball accelerates downward when she drops it:

- An object freely released in a gravitational field, according to Newton's law, will accelerate towards the center of mass.
- The earth has a gravitational field.
- Susie's ball constitutes a freely released object when it is dropped.
- Therefore Susie's ball accelerates toward the center of the earth (downward) when she drops it.

Note that the conclusion actually constitutes the phenomenon that needed explaining.

The problem frequently experienced with poor "science" is that the general premise (taken to be true) is the result of weak induction - or the result of the result of the result of weak induction. Even worse, such results are played as a statistical confirmation (via abduction) of a scientific theory, all the meanwhile feeding back into a "watertight deduction" that appears to be spotless.

Gravity looks like a pretty sound general premise, right? Well, that's because it has had centuries of experimental confirmation (courtesy of the scientific method). But what about other deductive arguments that look suspect? The "error" is normally not in the deductive argument itself - the argument can be perfectly valid and still be false. The falsity lies in the inadequate inductive basis of the general premise (or even the bridge premises).

Look for it. It is all too easy to find nowadays, especially in fields where the general premise is the brainchild of another premise that hasn't even been experimentally tested in years (several examples, *big* *bang*, caugh, come to mind).

-ExNihilo