Precursors Of Category Theory • 3

Act only according to that maxim by which you can at the same time will that it should become a universal law.

Immanuel Kant (1785)

C.S. Peirce • “On a New List of Categories” (1867)

§1.  This paper is based upon the theory already established, that the function of conceptions is to reduce the manifold of sensuous impressions to unity, and that the validity of a conception consists in the impossibility of reducing the content of consciousness to unity without the introduction of it.  (CP 1.545).

§2.  This theory gives rise to a conception of gradation among those conceptions which are universal.  For one such conception may unite the manifold of sense and yet another may be required to unite the conception and the manifold to which it is applied;  and so on.  (CP 1.546).

Cued by Kant’s idea regarding the function of concepts in general, Peirce locates his categories on the highest levels of abstraction able to provide a meaningful measure of traction in practice.  Whether successive grades of conceptions converge to an absolute unity or not is a question to be pursued as inquiry progresses and need not be answered in order to begin.

Resources

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Precursors Of Category Theory • 2

Thanks to art, instead of seeing one world only, our own, we see that world multiply itself and we have at our disposal as many worlds as there are original artists …

☙ Marcel Proust

When it comes to looking for the continuities of the category concept across different systems and systematizers, we don’t expect to find their kinship in the names or numbers of categories, since those are legion and their divisions deployed on widely different planes of abstraction, but in their common function.

Aristotle

Things are equivocally named, when they have the name only in common, the definition (or statement of essence) corresponding with the name being different.  For instance, while a man and a portrait can properly both be called animals (ζωον), these are equivocally named.  For they have the name only in common, the definitions (or statements of essence) corresponding with the name being different.  For if you are asked to define what the being an animal means in the case of the man and the portrait, you give in either case a definition appropriate to that case alone.

Things are univocally named, when not only they bear the same name but the name means the same in each case — has the same definition corresponding.  Thus a man and an ox are called animals.  The name is the same in both cases;  so also the statement of essence.  For if you are asked what is meant by their both of them being called animals, you give that particular name in both cases the same definition.  (Aristotle, Categories, 1.1a1–12).

Translator’s Note.  “Ζωον in Greek had two meanings, that is to say, living creature, and, secondly, a figure or image in painting, embroidery, sculpture.  We have no ambiguous noun.  However, we use the word ‘living’ of portraits to mean ‘true to life’.”

In the logic of Aristotle categories are adjuncts to reasoning whose function is to resolve ambiguities and thus to prepare equivocal signs, otherwise recalcitrant to being ruled by logic, for the application of logical laws.  The example of ζωον illustrates the fact that we don’t need categories to make generalizations so much as to control generalizations, to reign in abstractions and analogies which have been stretched too far.

References

  • Aristotle, “The Categories”, Harold P. Cooke (trans.), pp. 1–109 in Aristotle, Volume 1, Loeb Classical Library, William Heinemann, London, UK, 1938.
  • Karpeles, Eric (2008), Paintings in Proust, Thames and Hudson, London, UK.

Resources

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Precursors Of Category Theory • 1

A few years ago I began a sketch on the “Precursors of Category Theory”, tracing the continuities of the category concept from Aristotle, to Kant and Peirce, through Hilbert and Ackermann, to contemporary mathematical practice.  My notes on the project are still very rough and incomplete but I find myself returning to them from time to time.

Preamble

Now the discovery of ideas as general as these is chiefly the willingness to make a brash or speculative abstraction, in this case supported by the pleasure of purloining words from the philosophers:  “Category” from Aristotle and Kant, “Functor” from Carnap (Logische Syntax der Sprache), and “natural transformation” from then current informal parlance.

— Saunders Mac Lane • Categories for the Working Mathematician

Resources

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Survey of Precursors Of Category Theory • 5

A few years ago I began a sketch on the “Precursors of Category Theory”, tracing the continuities of the category concept from Aristotle, to Kant and Peirce, through Hilbert and Ackermann, to contemporary mathematical practice.  A Survey of resources on the topic is given below, still very rough and incomplete, but perhaps a few will find it of use.

Background

Blog Series

Categories à la Peirce

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Transformations of Logical Graphs • Discussion 1

Re: Laws of FormMauro Bertani

Dear Mauro,

The couple of pages linked below give the clearest and quickest introduction I’ve been able to manage so far when it comes to the elements of logical graphs, at least, in the way I’ve come to understand them.  The first page gives a lot of detail by way of motivation and computational implementation, so you could easily put that off till you feel a need for it.  The second page lays out the precise axioms or initials I use — the first algebraic axiom varies a bit from Spencer Brown for a better fit with C.S. Peirce — and also shows the parallels between the dual interpretations.

Additional Resources

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Transformations of Logical Graphs • 14

Semiotic Transformations

Re: Transformations of Logical Graphs • (8)(9)(10)(11)(12)(13)

Completing our scan of the Table in Episode 8, the last orbit up for consideration contains the logical graphs for the boolean functions f_{6} and f_{9}.

\text{Interpretive Duality} \stackrel{_\bullet}{} \text{Difference and Equality}

Interpretive Duality • Difference and Equality

The boolean functions f_{6} and f_{9} are known as logical difference and logical equality, respectively.  The values taken by f_{6} and f_{9} for each pair of arguments (x, y) in \mathbb{B} \times \mathbb{B} and the text expressions for their logical graphs are given in the following Table.

Truth Table • Difference and Equality

Resources

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Transformations of Logical Graphs • 13

Semiotic Transformations

Re: Transformations of Logical Graphs • (8)(9)(10)(11)(12)

Continuing our scan of the Table in Episode 8, the next orbit contains the logical graphs for the boolean functions f_{8} and f_{14}.

\text{Interpretive Duality} \stackrel{_\bullet}{} \text{Conjunction and Disjunction}

Interpretive Duality • Conjunction and Disjunction

The boolean functions f_{8} and f_{14} are called logical conjunction and logical disjunction, respectively.  The values taken by f_{8} and f_{14} for each pair of arguments (x, y) in \mathbb{B} \times \mathbb{B} and the text expressions for their logical graphs are given in the following Table.

Truth Table • Conjunction and Disjunction

Resources

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Transformations of Logical Graphs • 12

Semiotic Transformations

Re: Transformations of Logical Graphs • (8)(9)(10)(11)
Re: Interpretive Duality as Sign Relation • Orbit Order

Taking from our wallets an old schedule of orbits, let’s review the classes of logical graphs we’ve covered so far.

Self-Dual Logical Graphs

Four orbits of self‑dual logical graphs, x, y, \texttt{(} x \texttt{)}, \texttt{(} y \texttt{)}, were discussed in Episode 9.

Self-Dual Logical Graphs

The logical graphs x, y, \texttt{(} x \texttt{)}, \texttt{(} y \texttt{)} denote the boolean functions f_{12}, f_{10}, f_{3}, f_{5}, in that order.  The value of each function f at each point (x, y) in \mathbb{B} \times \mathbb{B} is shown in the Table above.

Constants and Amphecks

Two orbits of logical graphs called constants and amphecks were discussed in Episode 10.

Constants and Amphecks

The constant logical graphs denote the constant functions

f_{0} : \mathbb{B} \times \mathbb{B} \to 0 \quad \text{and} \quad f_{15} : \mathbb{B} \times \mathbb{B} \to 1.

  • Under \mathrm{Ex} the logical graph whose text form is “  ” denotes the function f_{15}
    and the logical graph whose text form is ``\texttt{(} ~ \texttt{)}" denotes the function f_{0}.
  • Under \mathrm{En} the logical graph whose text form is “  ” denotes the function f_{0}
    and the logical graph whose text form is ``\texttt{(} ~ \texttt{)}" denotes the function f_{15}.

The ampheck logical graphs denote the ampheck functions

f_{1}(x, y) = \textsc{nnor}(x, y) \quad \text{and} \quad f_{7}(x, y) = \textsc{nand}(x, y).

  • Under \mathrm{Ex} the logical graph \texttt{(} xy \texttt{)} denotes the function f_{7}(x, y) = \textsc{nand}(x, y)
    and the logical graph \texttt{(} x \texttt{)(} y \texttt{)} denotes the function f_{1}(x, y) = \textsc{nnor}(x, y).
  • Under \mathrm{En} the logical graph \texttt{(} xy \texttt{)} denotes the function f_{1}(x, y) = \textsc{nnor}(x, y)
    and the logical graph \texttt{(} x \texttt{)(} y \texttt{)} denotes the function f_{7}(x, y) = \textsc{nand}(x, y).

Subtractions and Implications

The logical graphs called subtractions and implications were discussed in Episode 11.

Subtractions and Implications

The subtraction logical graphs denote the subtraction functions

f_{2}(x, y) = y \lnot x \quad \text{and} \quad f_{4}(x, y) = x \lnot y.

The implication logical graphs denote the implication functions

f_{11}(x, y) = x \Rightarrow y \quad \text{and} \quad f_{13}(x, y) = y \Rightarrow x.

Under the action of the \mathrm{En} \leftrightarrow \mathrm{Ex} duality the logical graphs for the subtraction f_{2} and the implication f_{11} fall into one orbit while the logical graphs for the subtraction f_{4} and the implication f_{13} fall into another orbit, making these two partitions of the four functions orthogonal or transversal to each other.

Resources

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Transformations of Logical Graphs • 11

Semiotic Transformations

Re: Transformations of Logical Graphs • (8)(9)(10)

Continuing our scan of the Table in Episode 8, the next two orbits contain the logical graphs for the boolean functions f_{2}, f_{11}, f_{4}, f_{13}, in that order.  A first glance shows the two orbits have surprisingly intricate structures and relationships to each other — let’s isolate that section for a closer look.

\text{Interpretive Duality} \stackrel{_\bullet}{} \text{Subtractions and Implications}

Interpretive  Duality • Subtractions and Implications

  • The boolean functions f_{2} and f_{4} are called subtraction functions.
  • The boolean functions f_{11} and f_{13} are called implication functions.
  • The logical graphs for f_{2} and f_{11} are dual to each other.
  • The logical graphs for f_{4} and f_{13} are dual to each other.

The values of the subtraction and implication functions for each (x, y) \in \mathbb{B} \times \mathbb{B} and the text expressions for their logical graphs are given in the following Table.

Subtractions and Implications

Resources

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Transformations of Logical Graphs • 10

Semiotic Transformations

Re: Transformations of Logical Graphs • (4)(5)(6)(7)(8)(9)

After the four orbits of self‑dual logical graphs we come to six orbits of dual pairs.  In no particular order of importance, we may start by considering the following two.

  • The logical graphs for the constant functions f_{15} and f_{0} are dual to each other.
  • The logical graphs for the ampheck functions f_{7} and f_{1} are dual to each other.

The values of the constant and ampheck functions for each (x, y) \in \mathbb{B} \times \mathbb{B} and the text expressions for their logical graphs are given in the following Table.

Constants and Amphecks

Resources

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