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May 26, 2024, 9:48:33 AMMay 26

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 1

• https://inquiryintoinquiry.com/2024/05/25/precursors-of-category-theory-1-a/

All,

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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/VWY2Qq

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/25/precursors-of-category-theory-1-a/

All,

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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/VWY2Qq

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

May 27, 2024, 9:12:33 AMMay 27

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 2

• https://inquiryintoinquiry.com/2024/05/26/precursors-of-category-theory-2-a/

❝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

All,

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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/5wbQ91

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/26/precursors-of-category-theory-2-a/

❝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

All,

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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

May 28, 2024, 7:48:51 AMMay 28

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 3

• https://inquiryintoinquiry.com/2024/05/27/precursors-of-category-theory-3-a/

❝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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/LGJvkW

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/27/precursors-of-category-theory-3-a/

❝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 —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

May 28, 2024, 2:12:21 PMMay 28

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 4

• https://inquiryintoinquiry.com/2024/05/28/precursors-of-category-theory-4-a/

C.S. Peirce • “Prolegomena to an Apology for Pragmaticism” (1906)

❝I will now say a few words about what you have called Categories,

but for which I prefer the designation Predicaments, and which

you have explained as predicates of predicates.

❝That wonderful operation of hypostatic abstraction by which

we seem to create “entia rationis” that are, nevertheless,

sometimes real, furnishes us the means of turning predicates

from being signs that we think or think “through”, into being

subjects thought of. We thus think of the thought‑sign itself,

making it the object of another thought‑sign.

❝Thereupon, we can repeat the operation of hypostatic abstraction,

and from these second intentions derive third intentions. Does

this series proceed endlessly? I think not. What then are the

characters of its different members?

❝My thoughts on this subject are not yet harvested. I will only say

that the subject concerns Logic, but that the divisions so obtained

must not be confounded with the different Modes of Being: Actuality,

Possibility, Destiny (or Freedom from Destiny).

❝On the contrary, the succession of Predicates of Predicates is

different in the different Modes of Being. Meantime, it will be

proper that in our system of diagrammatization we should provide

for the division, whenever needed, of each of our three Universes

of modes of reality into “Realms” for the different Predicaments.❞

(CP 4.549).

The first thing to extract from the above passage is that Peirce's

Categories, for which he uses the technical term “Predicaments”, are

predicates of predicates. Considerations of the order Peirce undertakes

tend to generate hierarchies of subject matters, extending through what

is traditionally called the “logic of second intentions”, or what is

handled very roughly by “second order logic” in contemporary parlance,

and continuing onward through higher intentions, or higher order logic

and type theory.

Peirce arrived at his own system of three categories after a thoroughgoing

study of his predecessors, with special reference to the categories of

Aristotle, Kant, and Hegel. The names he used for his own categories

varied with context and occasion, but ranged from moderately intuitive

terms like “quality”, “reaction”, and “symbolization” to maximally

abstract terms like “firstness”, “secondness”, and “thirdness”.

Taken in full generality, k‑ness may be understood as referring to those

properties all k‑adic relations have in common. Peirce's distinctive claim

is that a type hierarchy of three levels is generative of all we need in logic.

Part of the justification for Peirce's claim that three categories

are necessary and sufficient appears to arise from mathematical facts

about the reducibility of k‑adic relations. With regard to necessity,

triadic relations cannot be completely analyzed in terms or monadic and

dyadic predicates. With regard to sufficiency, all higher arity k‑adic

relations can be analyzed in terms of triadic and lower arity relations.

Reference —

• Peirce, C.S. (1906), “Prolegomena to an Apology for Pragmaticism”,

The Monist 16, 492–546, CP 4.530–572.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/LY0pam

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/28/precursors-of-category-theory-4-a/

C.S. Peirce • “Prolegomena to an Apology for Pragmaticism” (1906)

❝I will now say a few words about what you have called Categories,

but for which I prefer the designation Predicaments, and which

you have explained as predicates of predicates.

❝That wonderful operation of hypostatic abstraction by which

we seem to create “entia rationis” that are, nevertheless,

sometimes real, furnishes us the means of turning predicates

from being signs that we think or think “through”, into being

subjects thought of. We thus think of the thought‑sign itself,

making it the object of another thought‑sign.

❝Thereupon, we can repeat the operation of hypostatic abstraction,

and from these second intentions derive third intentions. Does

this series proceed endlessly? I think not. What then are the

characters of its different members?

❝My thoughts on this subject are not yet harvested. I will only say

that the subject concerns Logic, but that the divisions so obtained

must not be confounded with the different Modes of Being: Actuality,

Possibility, Destiny (or Freedom from Destiny).

❝On the contrary, the succession of Predicates of Predicates is

different in the different Modes of Being. Meantime, it will be

proper that in our system of diagrammatization we should provide

for the division, whenever needed, of each of our three Universes

of modes of reality into “Realms” for the different Predicaments.❞

(CP 4.549).

The first thing to extract from the above passage is that Peirce's

Categories, for which he uses the technical term “Predicaments”, are

predicates of predicates. Considerations of the order Peirce undertakes

tend to generate hierarchies of subject matters, extending through what

is traditionally called the “logic of second intentions”, or what is

handled very roughly by “second order logic” in contemporary parlance,

and continuing onward through higher intentions, or higher order logic

and type theory.

Peirce arrived at his own system of three categories after a thoroughgoing

study of his predecessors, with special reference to the categories of

Aristotle, Kant, and Hegel. The names he used for his own categories

varied with context and occasion, but ranged from moderately intuitive

terms like “quality”, “reaction”, and “symbolization” to maximally

abstract terms like “firstness”, “secondness”, and “thirdness”.

Taken in full generality, k‑ness may be understood as referring to those

properties all k‑adic relations have in common. Peirce's distinctive claim

is that a type hierarchy of three levels is generative of all we need in logic.

Part of the justification for Peirce's claim that three categories

are necessary and sufficient appears to arise from mathematical facts

about the reducibility of k‑adic relations. With regard to necessity,

triadic relations cannot be completely analyzed in terms or monadic and

dyadic predicates. With regard to sufficiency, all higher arity k‑adic

relations can be analyzed in terms of triadic and lower arity relations.

Reference —

• Peirce, C.S. (1906), “Prolegomena to an Apology for Pragmaticism”,

The Monist 16, 492–546, CP 4.530–572.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

May 29, 2024, 12:00:27 PMMay 29

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 5

• https://inquiryintoinquiry.com/2024/05/29/precursors-of-category-theory-5-a/

❝A demonstration rests in a finite number of steps.❞

— G. Spencer Brown • Laws of Form

David Hilbert • “On the Infinite” (1925)

❝Finally, let us recall our real subject and, so far as the

infinite is concerned, draw the balance of all our reflections.

The final result then is: nowhere is the infinite realized;

it is neither present in nature nor admissible as a foundation

in our rational thinking — a remarkable harmony between being

and thought. We gain a conviction that runs counter to the

earlier endeavors of Frege and Dedekind, the conviction that,

if scientific knowledge is to be possible, certain intuitive

conceptions [Vorstellungen] and insights are indispensable;

logic alone does not suffice. The right to operate with the

infinite can be secured only by means of the finite.

❝The role that remains to the infinite is, rather, merely that

of an idea — if, in accordance with Kant’s words, we understand

by an idea a concept of reason that transcends all experience and

through which the concrete is completed so as to form a totality —

an idea, moreover, in which we may have unhesitating confidence

within the framework furnished by the theory that I have sketched

and advocated here.❞ (p. 392).

References —

• Hilbert, D. (1925), “On the Infinite”, pp. 369–392

in Jean van Heijenoort (1967/1977).

• van Heijenoort, J. (1967/1977), From Frege to Gödel :

A Source Book in Mathematical Logic, 1879–1931, Harvard

University Press, Cambridge, MA, 1967. 2nd printing, 1972.

3rd printing, 1977.

• Spencer Brown, G. (1969), Laws of Form, George Allen and Unwin,

London, p. 54.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/VrKAKZ

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/29/precursors-of-category-theory-5-a/

❝A demonstration rests in a finite number of steps.❞

— G. Spencer Brown • Laws of Form

David Hilbert • “On the Infinite” (1925)

❝Finally, let us recall our real subject and, so far as the

infinite is concerned, draw the balance of all our reflections.

The final result then is: nowhere is the infinite realized;

it is neither present in nature nor admissible as a foundation

in our rational thinking — a remarkable harmony between being

and thought. We gain a conviction that runs counter to the

earlier endeavors of Frege and Dedekind, the conviction that,

if scientific knowledge is to be possible, certain intuitive

conceptions [Vorstellungen] and insights are indispensable;

logic alone does not suffice. The right to operate with the

infinite can be secured only by means of the finite.

❝The role that remains to the infinite is, rather, merely that

of an idea — if, in accordance with Kant’s words, we understand

by an idea a concept of reason that transcends all experience and

through which the concrete is completed so as to form a totality —

an idea, moreover, in which we may have unhesitating confidence

within the framework furnished by the theory that I have sketched

and advocated here.❞ (p. 392).

References —

• Hilbert, D. (1925), “On the Infinite”, pp. 369–392

in Jean van Heijenoort (1967/1977).

• van Heijenoort, J. (1967/1977), From Frege to Gödel :

A Source Book in Mathematical Logic, 1879–1931, Harvard

University Press, Cambridge, MA, 1967. 2nd printing, 1972.

3rd printing, 1977.

• Spencer Brown, G. (1969), Laws of Form, George Allen and Unwin,

London, p. 54.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

May 31, 2024, 7:45:44 AMMay 31

to Cybernetic Communications, Laws of Form, Structural Modeling, SysSciWG

Precursors Of Category Theory • 6

• https://inquiryintoinquiry.com/2024/05/30/precursors-of-category-theory-6-a/

Hilbert and Ackermann • Principles of Mathematical Logic (1928)

❝For the intuitive interpretation on which we have hitherto

based the predicate calculus, it was essential that the

sentences and predicates should be sharply differentiated

from the individuals, which occur as the argument values

of the predicates. Now, however, there is nothing to prevent

us from “considering the predicates and sentences themselves

as individuals which may serve as arguments of predicates”.

❝Consider, for example, a logical expression of the form (x)(A → F(x)).

This may be interpreted as a predicate P(A, F) whose first argument

place is occupied by a sentence A, and whose second argument place

is occupied by a monadic predicate F.

❝A false sentence A is related to every F by the relation P(A, F);

a true sentence A only to those F for which (x)F(x) holds.

❝Further examples are given by the properties of “reflexivity”,

“symmetry”, and “transitivity” of dyadic predicates. To these

correspond three predicates: Ref(R), Sym(R), and Tr(R), whose

argument R is a dyadic predicate. These three properties are

expressed in symbols as follows:

• Ref(R) : (x)R(x, x),

• Sym(R) : (x)(y)(R(x, y) → R(y, x)),

• Tr(R) : (x)(y)(z)(R(x, y) & R(y, z) → R(x, z)).

❝All three properties are possessed by the predicate ≡(x, y)

(x is identical with y). The predicate <(x, y), on the other

hand, possesses only the property of transitivity. Thus the

formulas Ref(≡), Sym(≡), Tr(≡), and Tr(<) are true sentences,

whereas Ref(<) and Sym(<) are false.

❝Such “predicates of predicates” will be called

“predicates of second level”.❞ (p. 135).

❝We have, first, predicates of individuals, and these are classified

into predicates of different categories, or types, according to

the number of their argument places. Such predicates are called

“predicates of first level”.

❝By a “predicate of second level”, we understand one whose

argument places are occupied by names of individuals or by

predicates of first level, where a predicate of first level

must occur at least once as an argument. The categories, or

types, of predicates second level are differentiated according

to the number and kind of their argument places.❞ (p. 152).

Reference —

• Hilbert, D. and Ackermann, W., Principles of Mathematical Logic,

Robert E. Luce (trans.), Chelsea Publishing Company, New York, 1950.

1st published, Grundzüge der Theoretischen Logik, 1928. 2nd edition,

1938. English translation with revisions, corrections, and added notes

by Robert E. Luce, 1950.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://www.academia.edu/community/Lgrj0b

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

• https://inquiryintoinquiry.com/2024/05/30/precursors-of-category-theory-6-a/

Hilbert and Ackermann • Principles of Mathematical Logic (1928)

❝For the intuitive interpretation on which we have hitherto

based the predicate calculus, it was essential that the

sentences and predicates should be sharply differentiated

from the individuals, which occur as the argument values

of the predicates. Now, however, there is nothing to prevent

us from “considering the predicates and sentences themselves

as individuals which may serve as arguments of predicates”.

❝Consider, for example, a logical expression of the form (x)(A → F(x)).

This may be interpreted as a predicate P(A, F) whose first argument

place is occupied by a sentence A, and whose second argument place

is occupied by a monadic predicate F.

❝A false sentence A is related to every F by the relation P(A, F);

a true sentence A only to those F for which (x)F(x) holds.

❝Further examples are given by the properties of “reflexivity”,

“symmetry”, and “transitivity” of dyadic predicates. To these

correspond three predicates: Ref(R), Sym(R), and Tr(R), whose

argument R is a dyadic predicate. These three properties are

expressed in symbols as follows:

• Ref(R) : (x)R(x, x),

• Sym(R) : (x)(y)(R(x, y) → R(y, x)),

• Tr(R) : (x)(y)(z)(R(x, y) & R(y, z) → R(x, z)).

❝All three properties are possessed by the predicate ≡(x, y)

(x is identical with y). The predicate <(x, y), on the other

hand, possesses only the property of transitivity. Thus the

formulas Ref(≡), Sym(≡), Tr(≡), and Tr(<) are true sentences,

whereas Ref(<) and Sym(<) are false.

❝Such “predicates of predicates” will be called

“predicates of second level”.❞ (p. 135).

❝We have, first, predicates of individuals, and these are classified

into predicates of different categories, or types, according to

the number of their argument places. Such predicates are called

“predicates of first level”.

❝By a “predicate of second level”, we understand one whose

argument places are occupied by names of individuals or by

predicates of first level, where a predicate of first level

must occur at least once as an argument. The categories, or

types, of predicates second level are differentiated according

to the number and kind of their argument places.❞ (p. 152).

Reference —

• Hilbert, D. and Ackermann, W., Principles of Mathematical Logic,

Robert E. Luce (trans.), Chelsea Publishing Company, New York, 1950.

1st published, Grundzüge der Theoretischen Logik, 1928. 2nd edition,

1938. English translation with revisions, corrections, and added notes

by Robert E. Luce, 1950.

Resources —

Precursors Of Category Theory

• https://oeis.org/wiki/Precursors_Of_Category_Theory

Propositions As Types Analogy

• https://oeis.org/wiki/Propositions_As_Types_Analogy

Survey of Precursors Of Category Theory

• https://inquiryintoinquiry.com/2024/05/24/survey-of-precursors-of-category-theory-5/

Regards,

Jon

cc: https://mathstodon.xyz/@Inquiry/112502692087155139

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