Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

Post History

45%
+3 −4
Q&A Why does “unless” mean “if not”?

2 answers  ·  posted 4y ago by PSTH‭  ·  edited 3y ago by Peter Taylor‭

Question logic
#2: Post edited by user avatar Peter Taylor‭ · 2021-08-05T07:27:43Z (over 3 years ago)
A proposed edit tried to improve the typography with nbsp; this is a better fix
  • Harry Gensler. [*Introduction to Logic*](https://www.amazon.com/Introduction-Logic-Harry-J-Gensler/dp/1138910597) (2017 3 ed). p 169.
  • >“Unless” is also equivalent to “if not”; so we also could use “(∼B ⊃ D) (“If you
  • don’t breathe, then you’ll die”).”
  • Nicholas JJ Smith, [*Logic: The Laws of Truth*](https://www.amazon.com/Logic-Truth-Nicholas-J-J-Smith/dp/0691151636) (2012). p 115.
  • >The statement “P unless Q” means that if Q is not true, P is true—so we
  • translate it as $¬ \, Q→P$.
  • Using solely the original meaning of "unless" below, please expound why? How does definition 1 below ≡ if not? I know that definition 1 is obsolete, but I'm interested in the etymology. [*OED* Third Edition, June 2017](http://www.oed.com/view/Entry/215075). [Screenshot](https://i.stack.imgur.com/iZLrR.jpg).
  • > †**A.** adv. Only in conjunctional phrases followed by _than_ or _that_.
  • >
  • >1. Forming a conjunctional phrase introducing a case in which an exception to a preceding negative statement (expressed or implied) will or may exist: (not) on a less or lower condition, requirement, etc., _than_ (what is specified). _Obsolete_.
  • Harry Gensler. [*Introduction to Logic*](https://www.amazon.com/Introduction-Logic-Harry-J-Gensler/dp/1138910597) (2017 3 ed). p 169.
  • >“Unless” is also equivalent to “if not”; so we also could use “$({\sim}B \supset D)$ (“If you
  • don’t breathe, then you’ll die”).”
  • Nicholas JJ Smith, [*Logic: The Laws of Truth*](https://www.amazon.com/Logic-Truth-Nicholas-J-J-Smith/dp/0691151636) (2012). p 115.
  • >The statement “P unless Q” means that if Q is not true, P is true—so we
  • translate it as $¬ \, Q→P$.
  • Using solely the original meaning of "unless" below, please expound why? How does definition 1 below ≡ if not? I know that definition 1 is obsolete, but I'm interested in the etymology. [*OED* Third Edition, June 2017](http://www.oed.com/view/Entry/215075). [Screenshot](https://i.stack.imgur.com/iZLrR.jpg).
  • > †**A.** adv. Only in conjunctional phrases followed by _than_ or _that_.
  • >
  • >1. Forming a conjunctional phrase introducing a case in which an exception to a preceding negative statement (expressed or implied) will or may exist: (not) on a less or lower condition, requirement, etc., _than_ (what is specified). _Obsolete_.
#1: Initial revision by user avatar PSTH‭ · 2020-11-10T07:30:40Z (about 4 years ago)
Why does “unless” mean “if not”? 
Harry Gensler. [*Introduction to Logic*](https://www.amazon.com/Introduction-Logic-Harry-J-Gensler/dp/1138910597) (2017 3 ed). p 169. 

>“Unless” is also equivalent to “if not”; so we also could use “(∼B ⊃ D) (“If you
don’t breathe, then you’ll die”).”


Nicholas JJ Smith, [*Logic: The Laws of Truth*](https://www.amazon.com/Logic-Truth-Nicholas-J-J-Smith/dp/0691151636) (2012). p 115.

>The statement “P unless Q” means that if Q is not true, P is true—so we
translate it as $¬ \, Q→P$.


Using solely the original meaning of "unless" below, please expound why? How does definition 1 below ≡ if not? I know that definition 1 is obsolete, but I'm interested in the etymology. [*OED* Third Edition, June 2017](http://www.oed.com/view/Entry/215075). [Screenshot](https://i.stack.imgur.com/iZLrR.jpg).



>  †**A.** adv. Only in conjunctional phrases followed by _than_ or _that_.
> 
>1. Forming a conjunctional phrase introducing a case in which an exception to a preceding negative statement (expressed or implied) will or may exist: (not) on a less or lower condition, requirement, etc., _than_ (what is specified). _Obsolete_.