Archive for ‘mathematics’

April 27, 2017

Platonism, fictionalism and all that

by Neil Rickert

There was recently an interesting discussion of platonism and fictionalism as philosophies of mathematics.  This was at “The Electric Agora” blog.  I added a couple of comments myself.

Yesterday, I went back to take another look.  That was mostly to see if there were any additional comments.  And there were two, both by Robin Herbert.  But comments are now closed for that post.  So I’ll say something here.

First some links:

Both comments add to the discussion and are worth reading.

Is fictionalism true?

In his first comment, Robin says:

So the argument that fictionalism must be true because the axioms are only conventions appears to make the same mistake as saying the truth or falsity of “if A then B” depends on the truth or falsity of A.

To me, this seems weird.  I have said that I am a fictionalist.  I have never said that fictionalism is true.  I’m not at all sure that I know what it would even mean to say that fictionalism is true.

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February 1, 2015

Penelope Maddy interviewed

by Neil Rickert

Penelope Maddy was recently interviewed by 3am magazine (h/t Brian Leiter).  I found the interview interesting.

Maddy is a philosopher of mathematics.  In the past I have read some of her work related to set theory.  I very much disagreed with her philosophy, but her work was still worth reading.  She was very much into questions such as whether axioms are true.  That’s sometimes called “mathematical realism” because it is based on the idea that mathematics is saying something about the real world.

For myself, I could never make sense of mathematical realism.  As I saw it, axioms were neither true nor false.  I saw axioms as just useful assumptions whose consequences interested the mathematician.

It seems that Maddy has now moved away from that realism, so is adopting a view a bit closer to mine.  She now also doubts the Quine-Putnam indispensability thesis (that mathematical platonism is indispensable to physics).  Again, that is closer to my view.

I’m not at all sure that one’s philosophy of mathematics affects how one does mathematics.  But I did find it interesting to read of this evolution in her thinking.  And I’ll put this down as recommended reading for those interested in the philosophy of mathematics.

January 21, 2015

Against ontology – part 2

by Neil Rickert

My second example of why I don’t like ontology, is a TEDx talk by Kit Fine (h/t Brian Leiter).  In that talk, Fine discusses what is the fundamental nature of the being of numbers.

It’s a puzzle to me that anyone would suppose that numbers have any fundamental being.  It seems obvious that they do not.

Fine gives three possible versions of the nature of numbers.  The first is due to Frege and Russell, the second to von Neumann, the third to Cantor.  The only one of those that I find useful is von Neumann’s.  But I do not take it as being about the nature of numbers.  Rather, I take it as a useful way to model arithmetic within set theory.  I have always assumed (perhaps wrongly) that was why von Neumann proposed that definition.

Kit Fine seems to think that there are puzzles about numbers and mathematics, that can be resolved by understanding the nature of numbers.  He suggests that there is a puzzle as to why mathematics is so useful in science.  Others apparently also see that as a puzzle.  Fine asks (about numbers):

How can they be so far removed from the familiar world, yet so intimately connected to it?

Presumably, he thinks that understanding the fundamental nature of numbers will answer that question.

Numbers have no fundamental nature.  Perhaps knowing that will help Fine.

The usefulness of numbers and of mathematics is explained by how we use them, not by what they are.  The usefulness of numbers in science is explained by how scientists use them.

May 4, 2014

Coffee cups and donuts

by Neil Rickert

There’s a saying among mathematicians, that a topologist is someone who cannot tell the difference between a coffee cup and a donut.  I’ll discuss that in this post, and I’ll suggest implications beyond mathematics.

Usually, when we say this, we are thinking of the donut and the coffee cup as two-dimensional surfaces.  Once we go to the three-dimensional objects, nobody denies that the donut has a soft and spongy texture which makes it clearly different from a coffee cup.


Let’s start with a brief rundown on what is topology.  It is a branch of mathematics where we discuss ideas such as continuity, convergence, etc.  A classic example of convergence is with the sequence 0.9, 0.99, 0.999, …  We can see that the sequence gets closer and closer to 1, and we say that it converges to 1.  So topology has something to do with the geometric ideas of getting closer.  But it does so without needing a notion of metric (or distance).

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April 12, 2014

Is mathematics natural?

by Neil Rickert

While perusing the Uncommon Descent blog, I noticed a post

This seemed a strange thing to say.  It perhaps even involves what Gilbert Ryle would have called “a category mistake”.  Browsing through that post, I saw that it referred to an article in Aeon magazine

Clearly, professor Franklin and I have very different ways of looking at mathematics.  And that’s what I will be discussing in this post.

Mathematics and naturalism

Let’s start with that reference to “naturalism”.  Franklin adopts a philosophy that he describes as Aristotelian realism.  And it is in relation to that philosophy, that he makes his comment about naturalism.

Aristotelian realism stands in a difficult relationship with naturalism, the project of showing that all of the world and human knowledge can be explained in terms of physics, biology and neuroscience.

I’ve never fully understood what people mean by “naturalism”, nor have I understood the arguments about it that seem to be part of the culture wars.  The idea that the world and human knowledge can be explained in terms of physics, biology and neuroscience seems to me a non-starter — again, I see it as involving something like a category mistake.

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May 3, 2013

Truth and axioms in mathematics

by Neil Rickert

There’s been some discussion of truth in mathematics in the comments to my previous post.  Here, I want to expand a little on my view and express puzzlement at the idea that axioms are themselves true or false.

In response to a question, said “Actually, I take axioms to be neither true nor false, and I take the truth of mathematical theorems to be relative to the assumed axioms.”  Let me restate that in terms of the Peano axioms for ordinary arithmetic.

  1. The Peano axioms are neither true nor false.  Rather, they are definitional statements.  They define that part of mathematics known as Peano Arithmetic (or PA, or simply arithmetic).
  2. Theorems proved in PA are true in a relative sense.  Their truth is relative to the PA axioms.  They are true as used within PA, but perhaps not even meaningful outside of PA.

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December 25, 2012

Mathematics and logic

by Neil Rickert

Yesterday, Massimo Pigliucci posted on the relation between mathematics and logic:

so I though I would offer my opinion on that topic.  I see things differently from Massimo, but that’s probably just the different perspective as see by a mathematician (me) and a philosopher.

Massimo cites Peter Cameron (a mathematician) and Sharon Berry (a philosopher – actually a student of philosophy of mathematics).  Check Massimo’s post for the links.

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September 14, 2012

Mathematical Fictionalism

by Neil Rickert

Massimo Pigliucci has a post on mathematical platonism, so I thought it appropriate to discuss that in conjunction with my own version of mathematical fictionalism.

Pigliucci begins with three principle of platonism, which he takes from the SEP entry:

  1. Existence: There are mathematical objects;
  2. Abstractness: Mathematical objects are abstract;
  3. Independence: Mathematical objects are independent of intelligent agents and their language, thought, and practices.

Here’s the parallel principles for my version of fictionalism:

  1. Mathematical objects are useful fictions.  They have no actual existence, but it is useful to talk about them as if they existed.
  2. Mathematical objects are abstract.  I take this as a consequence of their being fictions.
  3. Mathematical objects are mental constructs, so are not strictly independent of the intelligent agents who talk about them.  However, if some alien intelligence exists — let’s call them Martians, to have a name — were to construct their own mathematics for reasons analogous to why we construct mathematics, then many of their mathematical fictions would have truth conditions analogous to those of our mathematics.

My fictionalist version of independence is weaker than the platonist version, though it seems adequate for mathematics.

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April 5, 2012

How I see logic

by Neil Rickert

I think it was in 4th grade elementary school, that I first heard of logic.  The teacher introduced it, with some examples to illustrate the use of logic.  I recall that it seemed rather easy to do logic.  All that I had to do was use clear thinking.  So I never did actually try to learn the rules of logic.  I just went by clear thinking, as appropriate.

I am posting this as one of the posts on my own views of philosophical topics.  No doubt my view of logic is partly shaped by the fact that I am a mathematician.  And, as a mathematician, I of course use a lot of logic.  But my basic view is still much the same as in 4th grade.  That is, I see logic as clear thinking.  It is a formalized or formalizable view of clear thinking, but it is nevertheless something that comes from clear thinking.

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December 5, 2011

Why mathematics is useful to science

by Neil Rickert

Philosophers, including philosophers of science, talk about representations.  For example, the statement “the cat is on the mat” might be a representation of one aspect of the world.  When mathematicians talk of representations, they think of a representation as a mapping of one space into another.  For the way that philosophers talk of representations, a mathematician might think of that as a mapping from reality to the space of linguistic expressions.

One way of having representations of the world is to come up with ad hoc methods of representing little bit of the world, and then tossing them together, willy nilly, to provide a more comprehensive representation of the world as a whole.  For want of a better term, I’ll call that way of representing the “willy nilly method” and I will refer to a representation result from such a method as a willy nilly representation.  The naming of houses by the first builder in my post “The parable of the three builders” could be considered a willy nilly representation.

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