Just In Case, If And Only If, And Formal Logic

[Tobriand]

Heya!

Just started a Logic course as part of Philosophy at uni, and I've come across an idea that, as yet, I haven't been able to reconcile between my thoughts and what the lecturer says. Seeing as the next lecture is on Monday, I thought I might post here and see what others think - maybe you can tell me why I'm wrong

Supposedly, in formal logic, at least, when translating from English, the phrases "just in case" and "if and only if" mean precisely the same thing. That is

A if and only if B
is supposedly the same as
A just in case B.

Which to my mind isn't in fact true. Take, as the basis, some random sentences.

"I will kill the koala if and only if I have a gun" ( A if and only if B )
versus
"I will kill the koala just in case I have a gun" (A just in case B)

To my mind, the two look completely different - the first translating, essentially to the two statements, "I will kill the Koala if I have a gun" and "There are no circumstances where I will kill the Koala if I do not have a gun". The second, on the other hand, seem to approximate to "I'll kill the Koala whether or not I have a gun". That is, when dealing with a "just in case" statement, only the first part actually seems to matter - the rest is merely why and wherefore you're performing the first action. The resultant statements are in fact, almost diametrically opposed to one another in what they mean!

Now, supposedly, I'm wrong. Which means somewhere in the above text is a huge fallacy. If anyone could direct me to it, I'd be most grateful; mostly logic is easy as pie, but somehow this bit is less so.

 

[mattmagoo]

wouldnt the second sentence, the just incase sentence be more like

"i will kill the koala in the case where I have the gun"

meaning you would not, for instance, kill it with a baseball bat

consider the second phrase "just in the case" instead of "just in case"

 

[iignotus]

Languages have no place in math. You've associated colloquialisms with a phrase; you need to abstract your thinking more.

Just in Case is the same as If and Only If. Just is the same as only in this usage in English. Therefore, your comparative sentence should be "I will kill the koala only in the case that I have a gun". I can't quite transliterate what you're thinking when you see the Just in Case clause, as I immediately recognize it as the correct logical equivalent, but I basically know where you're at.

This is being taught at a university?

 

[Goity]

If it was "just in the case" it would mean the same thing.

EDIT: beat me to it.

 

[c0ncept]

Nope, they are interchangable because they both refer to absolutes of circumstance.

1. you will kill the koala if and ONLY if you have a gun.

2. JUST in the case that you have a gun, you will kill the koala.

The (admittedly slight) variation between the two comes from the fact that "if and only if" deals with both cases (if you have a gun the koala gets it, if not then not) whereas the "just in case" doesn't actually state outright what will happen to the koala if you don't have a gun.

[edit] no, actually the 'just' is an absolute here as well. But I'll leave the above argument intact, is this what you were thinking?

 

[Tobriand]

Yeah, I think that's where I'd gone wrong. Typically, when I've come across the phrase "just in case" before in general usage its been in the style of "I'll go to his room just in case he's in" to imply several thing - that I'm looking for him (whoever he is), that he might be in his room, and that I'll go there to find out. As opposed to what it actually means in the logcal sense of "just in the case where X".

Thanks for the help - that clears up my conceptual muddle for today.

iignotus: Yeah, this is what they start use out with in the first lecture - albeit the one from the School of Philosophy as opposed to that of Science. But from what I've been told, most of the first year is extremely straightforward (read: no-one does any work - the phrase spoken by every second year student I've spoken to) across most of the board for arts subjects.

I've a friend doing Computer Science, which has a different logic course associated with it - THAT one jumps straight in with predicate logic and doesn't even bother with the bit we're doing in my course, from what I gathered.

 

[spray]

buy the simpson book applied logic, you'll be sorted.

its effectively talking about exclusive possibilities.

you are thinking about it too much.

i was never taught to think "just in case", ignore that translation and think "if and only if"

 

[Rico]

When people try to tell me, as they do on occasion, that Philosophy is a perfectly valid and useful degree - I will think of this thread.

 

[Esn]

When people try to tell me, as they do on occasion, that Philosophy is a perfectly valid and useful degree - I will think of this thread.

​

:lol:

The trouble is that there are many phrases in English which can be interpreted in more than one way. "If only if" is one of these. In ONE of the ways that it can be interpreted, it is correct to say that it is the same as "just in case". However, it can also be interpreted in several other ways which would mean something quite different.

"just in case" also changes meaning dramatically depending on where it is in the sentence.
"Let me tell you just in case I need a gun" vs. "Let me tell you I need a gun, just in case"

Yeah, I have proffesors teaching me silly rather silly things as well. Things like "without words there can be no ideas". My question is: If Beethoven goes "hmm, I have an idea... hm hm hm hmmmm!", would you then say "NOPE that's NOT an idea! HAH!"? If it's not an idea than what exactly do you call it?

Silly theorists... conveniently ignoring abundant contrary examples to make something sound simpler than it really is.

 

[c0ncept]

:/

language is a huge barrier to communication, how much better would the world be if you could express your exact meaning without being constrained by language. Anyone read the Invisibles? We need glossolalia...

 

[spray]

language is an amazing thing and is beautifully expressive

the problem is that few people really learn to utilise it to it's full extent