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Definition of mathematical object

  1. Apr 11, 2013 #1
    definition of "mathematical object"

    ...And "mathematical existence." Do these phrases have accepted definitions? Back when Dedekind was rejecting Cantor's transfinite ideas, could there have been a definition Cantor would refer to and say definitively "my (infinite) sets have mathematical existence because the criteria of the definition of mathematical object are satisfied"?

    There are many examples of mathematical objects. All structures are mathematical objects:
    http://math.chapman.edu/cgi-bin/structures?HomePage [Broken]

    A proof is also a mathematical object.

    Sets and categories are mathematical objects.

    Any formal system is a mathematical object.

    What is the common thread?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Apr 19, 2013 #2
    How about these for definitions:

    Mathematical object:
    That which is pointed to by a linguistic construct, known as an utterance, such that that utterance has at least one internally, logically-consistent interpretation.

    Mathematical existence:
    Something has mathematical existence if and only if it is a mathematical object.
  4. Apr 19, 2013 #3
    Maybe you would have more luck on a philosophy forum. All of this is not really mathematics...
  5. Apr 19, 2013 #4
    You're probably right except for the bit about this not being mathematics.
  6. Apr 19, 2013 #5
    It's not mathematics. No single mathematician cares about these things unless they're somehow interested in philosophy.
    I'm not saying your question is bad or boring. I'm just saying that it's not mathematics.
  7. Apr 19, 2013 #6


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    Can a mathematician be completely disinterested in philosophy? I'm not saying a mathematician will spend his time doing philosophy , but just to wonder what's going on at the most fundamental level of reality.
  8. Apr 19, 2013 #7
    I would define mathematics as the study of mathematical objects. So a mathematician would care about what that means iff they care what mathematics is. Admittedly, some of us don't care but logicians for example who treat mathematics as a mathematical object must care.

    This (the definition of mathematical object) is mathematics iff mathematics itself is a mathematical object and while I can understand your point of view, I disagree.

    Now that that is out of the way perhaps we can work towards defining what a mathematical object is.
  9. Apr 19, 2013 #8


    Staff: Mentor

    A mathematician can be interested in any number of things that aren't related to mathematics.
  10. Apr 19, 2013 #9
    Some mathematicians think that the study of mathematics is what's going on at the most fundamental level of reality.
  11. Apr 19, 2013 #10


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    Such an opinion would be a matter of philosophy. It has no mathematical content.
  12. Apr 19, 2013 #11
    Who? I haven't met any mathematician who thinks that way.
  13. Apr 19, 2013 #12
    @phoenixthoth - Mathematical objects are primitive notions of whatever formal system you happen to be using.

    Most mathematicians ostensibly use something like set theory. To them, a mathematical object is anything that can be encoded as a set. (This includes pairs, relations, functions, integers, the reals, etc).

    If I'm doing number theory, as the greeks might do, my objects would be just the integers.

    I'm I'm doing category theory, my objects are categorical objects and morphisms.

    If I'm doing type theory, my objects are types and terms and universes.

    But there is no absolute notion of what an object is. In set theory, people don't generally consider "proofs" to be mathematical objects. In type theory, they are. Category theory is often built on top of some other formalization (again, often set theory), and you end up working with "two levels" of objects. The same is also true in ZF set theory, since ZF is built "on top of" first order logic. Meanwhile, type theory is built "on top of" the lambda calculus. Of course, I can define lambda calculus in terms of set theory, or set theory in terms of type theory.

    In a way, it's very much the same as working with programming languages. Most languages have a notion of "object". But each language has their own definition. Most languages are turing complete and so (assuming the church-turing thesis) can bisumulate one another.

    But again, there is no absolute notion. You can go on with your turtle-tossing all you want, but every time, there's another turtle sitting underneath.
  14. Apr 19, 2013 #13
    Sounds like a great topic for another thread.

    If math isn't at all related to reality then it's basically the study of unicorns in the mathematician's basements; I refuse to believe that mathematics is not a study of the structure of reality.
    Last edited: Apr 19, 2013
  15. Apr 19, 2013 #14
    Yes and that's probably true of the process of defining anything: there are atomic words used in the definition. "There is no absolute notion," that is what I am trying to remedy....
  16. Apr 19, 2013 #15


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  17. Apr 19, 2013 #16
    Thanks, though I was really hoping to hear others chime in on what is a mathematical object. I will try there, too
  18. Apr 20, 2013 #17


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    Most of mathematics looks at variation: in other words how can we express variation for particular kinds of objects.

    This is expressed in the concept of a variable: it can be quite a range of structures including a numeric quantity, a map, a set, or something else but the key idea is that of variation.

    By understanding variation, we seek to classify and analyze it in order to understand how it affects our understanding for when things change or behave differently.

    This is true for everything from simple algebra to differential geometry: variation exists in all kinds of mathematical constructs.

    If there was no need for variation or variability, mathematics would not need to exist.
  19. Apr 20, 2013 #18


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    I don't see the point of defining "mathematical object", especially if this is just supposed to be an odd way of specifying what mathematics is. I think it takes an essay to explain what mathematics is.
  20. Apr 22, 2013 #19


    Staff: Mentor

    Much of mathematics is, or at least started out as something comparable to the study of unicorns. I doubt that many mathematicians would describe mathematics as studying the structure of reality.

    Some examples.
    Complex numbers, which have a real part and an imaginary part.
    Vector spaces of dimension higher than 3, including infinite-dimension spaces.
    Sphere packing in in fairly high-dimension spaces.
  21. Apr 23, 2013 #20


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    Even better example is the Banach-Tarski theorem. In this example the unicorns in question are non-measurable sets.
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