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August 20, 2012

Can we bring together a distant dual:

01. as is

10. as if

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From → Note to self

  1. Date: Sat, 21 Mar 2009
    From: Bill Lawvere
    Subject: categories: Re: Functions in programming

    […] Many of us have long instinctively believed that language should fit concepts and concepts should fit reality.


    F. William Lawvere, Professor emeritus
    Mathematics Department, State University of New York
    244 Mathematics Building, Buffalo, N.Y. 14260-2900 USA

  2. Divine Condemnation

    Date: Mon, 08 Apr 1996 22:50:05 -0500 (EST)
    From: F. W. Lawvere

    A contrast has been pointed out:
    working in a formal system
    reasoning about a formal system.

    Using both should lead in spiral fashion to both better formal systems and more knowledge about that which they describe. In this spirit we should surely expose the defects of a formal system rather than conceal them. The formal system may need to be changed. It would be one-sided to only “work in” a system, accepting it as a divine condemnation that we have to endure.

    The objective necessity that every map has both a domain and a codomain is one of the great principles of category theory. […] Hence the answer to both of the questions
    Does topos logic correspond to type theory?
    Does topos logic correspond to set theory?
    is NO. Both were earlier, partially successful attempts to make explicit some “necessary laws of the development of thinking in all the areas of mathematics”.

    […] For mathematics, freedom came from the recognition of that necessity: the foundational role was thus abandoned in practice by st [set theory] which promoted the “freedom” allegedly deriving from ignoring codomains, while tt [type theory], though recognizing some codomains (as types), gets entangled in the “flexibility” of refusing to declare variables, i.e. to specify domains.

    A set in a topos is neither a type nor not a type: there are sets of exactly the right size to be susceptible of being wired up as memory banks which serve as power types or function types (or more specific mathematically-oriented objects) relative to some given sets, the wiring being suitable maps which serve as evaluations, inclusions, etc.

    A set in a topos is not a von Neumann “set” either; it has a cohesiveness due to the incidence relations between its elements (right actions, pullbacks) so is a “Menge” not due to an excessive and irrelevant structure but to a structure adapted to the mathematical category of cohesiveness at hand.

    We carry the inclusions around only as long as we need them. Already Gauss pointed out that when a subset (i.e. an inclusion map) arises, it may be very significant to study the domain in its own intrinsic self, but this is difficult to make precise in st or tt. Of course “subset” is not a binary relation between sets but a given map, a mathematical necessity that needs to be recognized by any truly flexible formalization in a way coherent enough to work in. Given two inclusion maps b, c with the same codomain A, it is clear what is a proof that “b is included in c” as subsets of A, and given any element x of A (i.e. any map with codomain A), a proof that “x belongs to b” is formally the same kind of thing. Hence by composing proofs we can always conclude that x belongs to c, independently of whether these subsets arose by equalizing some maps P with domain A.

    […] Formal systems are subjective instruments for describing and clarifying such presentations. […]

    In the end it will surely be simpler, leading to greater freedom and fewer complications, to explicitly take the objectively necessary into account, rather than to succumb to a naive belief in the “freedom” to neglect some essential ingredient. There need not be an inevitable mismatch between useable formal systems and the mathematical structures they strive to present.

  3. Subject: Re: Perception, intuition & reason, Date: 02 May 2010, From: Andree Ehresmann, To: posina

    Dear Posina,

    You asked about a mathematical construct uniting geometry and logic.

    A topos contains features of both domains, however I don’t see how it could be applied to conscious perceptual experience.

    In Chapters 9 and 10 of our book where our model MENS of a neural and cognitive system is developed, this problem is analysed as follows:.

    Perception of a ‘concrete’ item S is decomposed:
    1. Formation or recognition of a record of S (geometric part: Chapter 9, Section 5):
    a record of S is constructed (by a complexification process) as a category-neuron binding (meaning colimit, or inductive limit, of) patterns of neurons activated by different features of S.
    2. Formation of a “concept” (logic part: Chapter 10, Section 1):
    For ‘concrete’ items S, the symbol classifying the invariance class of S (which we call “concept” but seems close to your “percept”) is constructed as a projective limit of the internal trace of S.

    The concrete concepts form a basis B of the “semantic memory” Sem; more abstract concepts in Sem are obtained from B through iterated binding and classifying processes. For instance “intuition” and “reason” are such abstract concepts, and your “equality” could mean that Perception is obtained by binding them in Sem.

    The conscious perceptual experience of an item S is a particular conscious process, triggered by the presentation of S or the recall of its record. We propose an interpretation of such a process in Chapter 10, Section 3; or, in a more developed way, in our paper: “MENS, a mathematical model for cognitive systems, Journal of Mind Theory 0-2, 129-180″ which is available on my site
    It would be interesting to see how these general ideas agree with experimental data.

    With all my best wishes for your research
    Warm regards

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