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

37%
+1 −3
Q&A Are these introductory logic textbooks wrong to teach ‘unless’ = ‘or’? [duplicate]

0 answers  ·  posted 10mo ago by 8500 Ward‭  ·  closed as duplicate 10mo ago by Peter Taylor‭

Question logic
#2: Question closed by user avatar Peter Taylor‭ · 2024-01-26T10:16:15Z (10 months ago)
#1: Initial revision by user avatar 8500 Ward‭ · 2024-01-25T19:06:06Z (10 months ago)
Are these introductory logic textbooks wrong to teach ‘unless’ = ‘or’? 
[Colin Fine](https://english.stackexchange.com/users/547/colin-fine) answered that

>[Unless" does not equal "or" 'directly and intuitively'.]( https://english.stackexchange.com/a/296700)


This contradicts the textbooks beneath. Who is correct?

>[Usually, "P unless Q" is "symbolized as P ∨ Q.]( https://philosophy.stackexchange.com/a/32372) Stephen Cole Kleene, [Mathematical logic](https://books.google.it/books?id=q-YEuuZ_j8EC&pg=PA64) (1967 - Dover ed 2002), page 64.

![](https://i.imgur.com/9lInApk.jpg)

Lande N.P. _Classical logic and its rabbit-holes: A first course_ (2013), pages 55-7.

>The wedge symbol is used to translate “or” and “unless.” A previous chapter explained that “unless” is equivalent in meaning to “if not.” This equivalence holds in propositional logic as well, but in propositional logic it is usually simpler to equate “unless” with “or.” For example, the statement “You won’t graduate unless you pass freshman English” is equivalent to “Either you pass freshman English or you won’t graduate” and also to “If you don’t pass freshman English, then you won’t graduate.” As the next section demonstrates, the wedge symbol has the meaning of “and/or”—that is, “or” in the inclusive sense. Although “or” and “unless” are sometimes used in an exclusive sense, the wedge is usually used to translate them as well.

Hurley P. _A Concise Introduction to Logic_ (13 edn, 2018), page 319.

> Translate “unless” as “or.”

Gensler H. _Introduction to Logic_ (3 edn 2017), 132.

> In addition, the word “unless” sometimes functions like the word “or.” For example, the statement “You can’t go to the party unless you clean your room,” can be rewritten as “Either you clean your room or you can’t go to the party.”

Baronett S. _Logic_ (5 edn 2022), 318