Philosophy 160
Spring 2004

Duhem/Quine Theses

Duhem Thesis:
An experiment in physics can never condemn an isolated hypothesis but only a whole theoretical group.

Why?

Another claim from Duhem: A crucial experiment (eliminating all hypotheses save one) is impossible because you can never be sure you’ve enumerated all the hypotheses capable of explaining a group of phenomena.

Quine’s Thesis:
Hypotheses cannot be refuted by observation and experiment when taken in isolation, but only when considered as parts of theoretical groups.

Another central claim: Our scientific theories are underdetermined by our experience.  There are lots of ways the world could be (and thus, many equally good theories we could hold to account for that world) which are consistent with our experience.

Quine’s dramatic claim:
“Any statement can be held to be true come what may, if we make drastic enough adjustments elsewhere in the system.” (43)

What do these claims have to do with the two dogmas Quine criticizes?

First, recall the dogmas:

1.  Analytic/synthetic cleavage: There is a fundamental difference between synthetic truths (those grounded in fact) and analytic truths (those grounded in meanings independently of matters of fact).
2. Reductionism:  Meaningful statements can be re-expressed in terms which refer to immediate experience.


Both of these positions fly in the face of the holism Quine advocates.  He says you can’t test a hypothesis in isolation.  And he says changes in one hypothesis can prompt changes throughout the whole logical structure of a scientific theory.

What does this have to do with that stuff found on Twin Earth?

The central question of the thought experiment was whether the stuff brought back from Twin Earth is water.  The puzzle is how exactly we’re supposed to make this determination.

In 1600, the only ways of telling whether or not something is water involve behaviors like freezing and boiling, dissolving salt or sugar, quenching thirst, watering plants, etc.  Based on the available evidence, it’s reasonable for the scientist in 1600 to say that the stuff from Twin Earth is water.

By 1785, there is another technique available for studying the stuff from Twin Earth: elemental analysis.  This technique tells us that the elemental composition of the water collected on Earth is two parts H to one part O (or H2O), while the elemental composition of the stuff from Twin Earth is something else (call it XYZ).

So, we now have a technique that allows us to distinguish between the stuff from Earth and the stuff from Twin Earth.  (However, this is the only detectable difference; in all other ways they behave the same.)  Does this help us decide whether the stuff from Twin Earth is water?

Hypotheses:
1. Water is the stuff found in rivers, lakes, streams, and aqueducts that humans drink, cook with, bathe in, swim in, etc.
2. Water displays certain regular behaviors (boiling under specified conditions, freezing under certain specified conditions, dissolving particular amounts of certain substances, etc.).
3. Although water from the ocean, water from a stream, water from a well, rainwater, etc., may differ in their impurities (salt, mud, etc.), they all count as water; that is, the substance containing this different impurities is the same.
4. Water’s behavior is a result of what it is made of.
5. If two samples display different microstructure (e.g., different elemental composition), they must be samples of different substances.
6. Substances with different microstructures will display different macroscopic behavior.


Given the results of the elemental analyses in 1785, we probably can’t commit to all of these hypotheses.  The Earth stuff and the Twin Earth stuff have different microstructures but the same macroscopic behavior.  So, which of these hypotheses should we keep?  Which should we abandon?

If science is holistic, then scientists make choices — rather than being forced by the data to a single conclusion, they have to use the data to decide how to update their hypotheses and concepts.

Two obvious choices in the 1785 analysis of Earth water and Twin Earth stuff:
1. Conclude that water and the Twin Earth stuff are different substances because they have different microstructures (H2O and XYZ).
2. Conclude that a single microstructure is not essential to making something water (since water and the Twin Earth stuff are identical in all other respects).

After the discovery of naturally occurring XYZ in Southern Hemisphere waterways, scientists might decide to reconsider an early decision that H2O is water and XYZ is not.

Maybe it all comes back to meanings …

What is it that fixes the meaning of “water”?  Here are two possibilities:

1. “Baptism”:  We point at the stuff in the world and say, “This stuff here is water.”  In the naming, though, we usually mean to include the other stuff that is relevantly similar (e.g., the stuff in other lakes, rivers, streams, etc., not just the stuff in this bucket).
2. “Description”:  We enumerate a set of properties and say, “Water is whatever substance has these specified properties.”  Here, how we specify the properties will determine what counts as water and what doesn’t.  Also, it is entirely possible that we may list a set of properties that no substance has.
Of course, science takes as its purpose a description of the stuff (like water) in our world; this can lead to potential confusion about what we mean by a term like “water”!

Science can give us more information about stuff in our world (e.g., the water in the Seine is H2O).  But can science do more than tell us facts about the stuff we call water?  Does science get to define what “water” properly means?  (For example, can science tell the folks in Australia that they were wrong to call the XYZ in their lakes “water”?)  Why or why not?  And what other changes in our understanding of the world might these redefinitions require?


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