1. Flight from Dualism

1. The Flight from Dualism

Redefining the definition of materialism

a. What things count as physical?

b. What does it mean for them to be explanatorily sufficient?

Defining the physical

Physical things are the things that occur in a physical theory.

Define physical sciences? Can’t include psychology or its objects, like ‘beliefs’, become physical.

We know that science is incomplete – but we hope not incomplete in the kinds that it deals with.

Also, incompleteness is probably at a level well below what we think is needed to explain mentality.

The core idea versus getting the definition exactly ‘right’

The materialist holds that mental is produced from physical by combination of physical parts. That’s clear enough even if we can’t be quite sure about what counts as ‘physical.’

Supervenience

Introduction to supervenience

A materialist claims that the physical story is complete (and the dualist denies it.) The materialist must say that mental facts are somehow explicable in physical terms.

One way to express this without being too specific is to say that the mental supervenes on the physical

Supervenience and completeness

Hair distribution determines baldness

You are bald or not because of the distribution of hairs on your head. But they are not the cause of your baldness – that would be a medical thing. Facts about them they logically dertermine facts about your baldness.

Supervenience and determination

We can say that there is no difference in baldness without a difference in hair distribution.

There are no facts about baldness that are not facts about hair distribution.

(Note the asymmetry here.)

Supervenience, inclusion, and making true

This is a common relationship. Eg. motion supervenes on change in position – two objects identical in terms of change of position must be identical in terms of motion.

Materialists say two objects identical in physical properties must be identical in mental; or, there can be no variation in mental properties without a variation in physical properties.

Supervenience and possible worlds

We can be more precise by talking in PW terms. PW are also generally useful, so we’ll give a more general introduction than is necessary right now.

Possible Worlds: An Introduction

Possible worlds as complete ways things might be

A Possible World is a way things could have been.

PW are a way of talking about how things could have been but aren’t.

(A PW is an alternative universe. It’s not talking about other worlds like Mars.)

(The Actual world is also a PW. We abbreviate it @.)

Possible worlds in everyday talk

We talk about possibilities a lot. PW make this sort of talk more disciplined.

It’s possible that I could have wine means there’s a PW where I do have wine.

PW are complete. In each world where I have wine it is either true or false that there are 34,000 zebras.

There are various meanings for possibility:

Logically: alternatives are limited only by laws of logic. In no LP PW are bachelors married.

Nomologically: limited by laws of Nature. In no NP PW is light slower than sound..

Explication in terms of possible worlds

Necessary truth

Necessarily true = true in all PW

Possibly true = true in at least one PW

Necessarily false = true in no PW

Contingent = not NT or NF

Propositions

Sentence S expresses the proposition P : P is the set of worlds in which S is true.

Isn’t the same as meaning. (Note: all NT and NF sentences express the same propositions.)

[Note that the textbook’s use of this term is not regular or self-consistent.]

Entailment

S entails T iff it is necessary that if S then T

Proposition of S is a subset of the proposition of T

Essential and accidental properties

P is an accidental property of X if there are PW in which X doesn’t have P

P is an essential property of X if there are no PW in which X doesn’t have P

*Supervenience and possible worlds

Express supervenience in terms of PW by a global supervenience thesis.

Eg. For all W1 and W2, if W1 and W2 are exactly the same wrt hair then they are the same wrt baldness

*Materialism and supervenience

Finding the right supervenience thesis for materialism

What specific global supervenience thesis would materialists approve?

1. For all W1 and W2, if W1 and W2 are exactly the same physically then they are the same mentally

No. Materialists are interested in @, not in other PW. Other worlds may be non-materialist.

2. For any W, if W and @ are exactly the same physically then they are the same mentally

No. W may be a physical duplicate but may also have non-physical stuff affecting mentality.

3. For any W, if W is a minimal physical duplicate of @ then they are the same mentally

(Minimal means nothing is specified as in W apart from @’s physical stuff.)

Yes. More directly, suppose (3) is false, i.e. @ and W differ mentally, but W is a minimal physical duplicate of @; then @ and W must have different natures; then @ must have properties other than those minimally physically duplicated in W.

*Making true and the varieties of materialism

(3) can be stated in terms of entailments: physical nature entails mental nature.

But entailment only holds between sentences, so rephrase that as: sentence S describing the physical nature of @ entails every sentence T describing some mental fact about @.

Materialism holds that physical facts are what make statements about mental things true or false.

Different varieties of materialism differ on what facts are relevant and how.

*Some warnings and physical properties revisited

Intra-world supervenience theses

A global supervenience thesis is different from an intra-world supervenience thesis.

An intra-world ST for A and B would be something like: if X and Y are identical in W wrt A then X and Y are identical in W wrt B.

E.g. If X and Y are both 6’ tall then X and Y are both in the tallest 25% of the population.

The meanings of ‘physical property’

Can we clarify the notion of ‘physical properties’ for materialism any more?

Current science

Can it be properties in current science?

No. Current science is incomplete and any revisions would then be non-physical by definition.

Final science

Can it be properties in a completed science?

No. We don’t know what they’ll be.

Also, final science explains everything, so it will include mental objects, so they are made physical by definition.

Two ways of refining final science

1. Methodological. Final science is the best theory that can be found using the scientific method.

Now all we need to do is specify the ‘scientific method’ for all time.

2. Uniformity. Final science is the best theory that explains all the things that we declare to be non-mental. What occurs in that theory we declare to be physical. If mental things are also explained then Nature is uniform; otherwise dualism is true.

Problems for the second definition

Rules out Panpsychism by definition.

If rocks are declared to be non-mental, but rocks do in fact have a mentality, then final science will include mental properties, and so mental properties are physical. But that is not in the spirit of materialism..

Defining non-physical properties by modes of access

Science can only treat things which have causal effects, and properties defined in terms of causal roles are scientifically accessible.

There may be properties that are experientially accessible but not scientifically.

Given this division one might call the former properties the physical properties and the latter non-physical.

But not necessarily: why not just say that the latter are just physical properties that aren’t scientifically accessible.

Return to the simple definintion

Since these clarifications fail, we’ll stick with the vague understanding we had earlier, and hope it’s ok.

These references to the physical lead us to call materialism also physicalism – but there are other meanings for the latter term too.

Physicalism and physics-alism

Using the term ‘physicalism’ may also imply that it is being claimed that only the properties occurring in Physics are relevant, as opposed to accepting all the sciences.