The Mean and the Variance as Dual Concepts in a Fundamental Duality

A basic duality arises throughout the mathematical and natural sciences. Traditionally, logic is thought to be based on the Boolean logic of subsets, but the development of category theory in the mid-twentieth century shows the duality between subsets and partitions (or equivalence relations). Hence...

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Main Author: David Ellerman
Format: Article
Language:English
Published: MDPI AG 2025-06-01
Series:Axioms
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Online Access:https://www.mdpi.com/2075-1680/14/6/466
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author David Ellerman
author_facet David Ellerman
author_sort David Ellerman
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description A basic duality arises throughout the mathematical and natural sciences. Traditionally, logic is thought to be based on the Boolean logic of subsets, but the development of category theory in the mid-twentieth century shows the duality between subsets and partitions (or equivalence relations). Hence, there is an equally fundamental dual logic of partitions. At a more basic or granular level, the elements of a subset are dual to the distinctions (pairs of elements in different blocks) of a partition. The quantitative version of subset logic is probability theory (as developed by Boole), and the quantitative version of the logic of partitions is information theory re-founded on the notion of logical entropy. The subset side of the duality uses a one-sample (or one-element) approach, e.g., the mean of a random variable; the partition side uses a two-sample (or pair-of-elements) approach. This paper gives a new derivation of the variance (and covariance) based on the two-sample approach, which positions the variance on the partition and information theory side of the duality and thus dual to the mean.
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spelling doaj-art-8d0e8c5e180d4ca5b698f996866458622025-06-25T13:28:27ZengMDPI AGAxioms2075-16802025-06-0114646610.3390/axioms14060466The Mean and the Variance as Dual Concepts in a Fundamental DualityDavid Ellerman0Independent Researcher, 1000 Ljubljana, SloveniaA basic duality arises throughout the mathematical and natural sciences. Traditionally, logic is thought to be based on the Boolean logic of subsets, but the development of category theory in the mid-twentieth century shows the duality between subsets and partitions (or equivalence relations). Hence, there is an equally fundamental dual logic of partitions. At a more basic or granular level, the elements of a subset are dual to the distinctions (pairs of elements in different blocks) of a partition. The quantitative version of subset logic is probability theory (as developed by Boole), and the quantitative version of the logic of partitions is information theory re-founded on the notion of logical entropy. The subset side of the duality uses a one-sample (or one-element) approach, e.g., the mean of a random variable; the partition side uses a two-sample (or pair-of-elements) approach. This paper gives a new derivation of the variance (and covariance) based on the two-sample approach, which positions the variance on the partition and information theory side of the duality and thus dual to the mean.https://www.mdpi.com/2075-1680/14/6/466fundamental subsets–partitions dualitylogic of subsetslogic of partitionslogical entropyvariancecovariance
spellingShingle David Ellerman
The Mean and the Variance as Dual Concepts in a Fundamental Duality
Axioms
fundamental subsets–partitions duality
logic of subsets
logic of partitions
logical entropy
variance
covariance
title The Mean and the Variance as Dual Concepts in a Fundamental Duality
title_full The Mean and the Variance as Dual Concepts in a Fundamental Duality
title_fullStr The Mean and the Variance as Dual Concepts in a Fundamental Duality
title_full_unstemmed The Mean and the Variance as Dual Concepts in a Fundamental Duality
title_short The Mean and the Variance as Dual Concepts in a Fundamental Duality
title_sort mean and the variance as dual concepts in a fundamental duality
topic fundamental subsets–partitions duality
logic of subsets
logic of partitions
logical entropy
variance
covariance
url https://www.mdpi.com/2075-1680/14/6/466
work_keys_str_mv AT davidellerman themeanandthevarianceasdualconceptsinafundamentalduality
AT davidellerman meanandthevarianceasdualconceptsinafundamentalduality