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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Transformations of Logical Graphs • 9

Semiotic Transformations

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

Last time we took up the four singleton orbits in the action of T on X and saw each consists of a single logical graph which T fixes, preserves, or transforms into itself.  On that account those four logical graphs are said to be self‑dual or T‑invariant.

In general terms, it is useful to think of the entitative and existential interpretations as two formal languages which happen to use the same set of signs, each in its own way, to denote the same set of formal objects.  Then T defines the translation between languages and the self‑dual logical graphs are the points where the languages coincide, where the same signs denote the same objects in both.  Such constellations of “fixed stars” are indispensable to navigation between languages, as every argot‑naut discovers in time.

Returning to the case at hand, where T acts on a selection of 16 logical graphs for the 16 boolean functions on two variables, the following Table shows the values of the denoted boolean function f : \mathbb{B} \times \mathbb{B} \to \mathbb{B} for each of the self‑dual logical graphs.

Self-Dual Logical Graphs

The functions indexed here as f_{12} and f_{10} are known as the coordinate projections (x, y) \mapsto x and (x, y) \mapsto y on the first and second coordinates, respectively, and the functions indexed as f_{3} and f_{5} are the negations (x, y) \mapsto \tilde{x} and (x, y) \mapsto \tilde{y} of those projections, respectively.

Resources

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Transformations of Logical Graphs • 8

Semiotic Transformations

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

Turning again to our Table of Orbits let’s see what we can learn about the structure of the sign relational system in view.

As we saw in Episode 2, the transformation group T = \{ 1, t \} partitions the set X of 16 logical graphs and also the set O of 16 boolean functions into 10 orbits, all together amounting to 4 singleton orbits and 6 doubleton orbits.

Points in singleton orbits are called fixed points of the transformation group T : X \to X since they are left unchanged, or changed into themselves, by all group actions.  Viewed in the frame of the sign relation L \subseteq O \times X \times X, where the transformations in T are literally translations in the linguistic sense, these T-invariant graphs have the same denotations in O for both Existential Interpreters and Entitative Interpreters.

\text{Interpretive Duality as Sign Relation} \stackrel{_\bullet}{} \text{Orbit Order}

Interpretive Duality as Sign Relation • Orbit Order

Resources

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