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In the same Unicode block is "2129 ℩ TURNED GREEK SMALL LETTER IOTA" with explanation "unique element fulfilling a description (logic)". That seems a ridiculou

In the same Unicode block is "2129 ℩ TURNED GREEK SMALL LETTER IOTA" with explanation "unique element fulfilling a description (logic)". That seems a ridiculous choice for a symbol — turning one of the most symmetrical letters upside down! Background: https://philosophy.stackexchange.com/questions/51563/what-is-the-symbol-in-formal-logic https://philosophy.stackexchange.com/questions/51563/what-is...

Archelaos 2y ago
It could be motivated by the fact that Russell and Whitehead needed a symbol for printing that the printer had in his type case but could not be confused with anything else. Taking a iota and simply turning it upside down would then be a rather ingenious idea. But that is just my speculation ...
- eesmith 2y ago
  https://math.stackexchange.com/questions/1885938/whats-meaning-of-the-inverted-greek-letter-iota-%CE%B9-in-principia-mathematica-i https://math.stackexchange.com/questions/1885938/whats-meani... says 'in the article Frege, Peano and Russell on Descriptions: a Comparison, Francisco A. Rodríguez-Consuegra tracks down the source to Peano's Studii di logica matematica (1897) as where the operator first appears' That page in 'Studii di logica matematica' appears to be https://archive.org/details/peano-studii-di-logica-matematica/page/18/mode/2up https://archive.org/details/peano-studii-di-logica-matematic... . It also uses an upside-down C and upside-down E.
  - Archelaos 2y ago
    And the Lambda looks like an upside-down V. The bases of all these upside-down letters do not match the baseline of the text. Obviously there were no special upside-down moveable types available of freshly cast for this book. Peano had to creatively repurpose what types were available.
- masfuerte 2y ago
  There are loads of examples of this, e.g. ∀ and ∃, but iota is a really poor choice.
schoen 2y ago
In the font on my phone it looks confusingly reminiscent of Hebrew vav.

Archelaos 2y ago

It could be motivated by the fact that Russell and Whitehead needed a symbol for printing that the printer had in his type case but could not be confused with anything else. Taking a iota and simply turning it upside down would then be a rather ingenious idea. But that is just my speculation ...

eesmith 2y ago
https://math.stackexchange.com/questions/1885938/whats-meaning-of-the-inverted-greek-letter-iota-%CE%B9-in-principia-mathematica-i https://math.stackexchange.com/questions/1885938/whats-meani... says 'in the article Frege, Peano and Russell on Descriptions: a Comparison, Francisco A. Rodríguez-Consuegra tracks down the source to Peano's Studii di logica matematica (1897) as where the operator first appears' That page in 'Studii di logica matematica' appears to be https://archive.org/details/peano-studii-di-logica-matematica/page/18/mode/2up https://archive.org/details/peano-studii-di-logica-matematic... . It also uses an upside-down C and upside-down E.
- Archelaos 2y ago
  And the Lambda looks like an upside-down V. The bases of all these upside-down letters do not match the baseline of the text. Obviously there were no special upside-down moveable types available of freshly cast for this book. Peano had to creatively repurpose what types were available.
masfuerte 2y ago
There are loads of examples of this, e.g. ∀ and ∃, but iota is a really poor choice.

schoen 2y ago

In the font on my phone it looks confusingly reminiscent of Hebrew vav.