Conditional statements that use "unless" Forum
- DSman
- Posts: 1385
- Joined: Wed Jun 27, 2012 4:27 am
Conditional statements that use "unless"
For some reason I always have to stop and think about these types of conditional statements which just wastes time on LG so I want to write down a bunch and please correct me.
1. "A is 2nd unless B is 3rd" This would be:
If B is 3rd then A is not second OR
If A is 2nd then B is not 3rd
2. "A is not 2nd unless B is 3rd"
If A is 2nd then B is 3rd
If B is not 3rd then A is not 2nd
3. A comes before B unless E is before F
IF E is before F then A is after B
If A is before B then E is after F
4. A cannot be before B unless E is before F
If A is before B then E is before F
If E is after F then A is after B
Do i have these down correctly? Thanks.
1. "A is 2nd unless B is 3rd" This would be:
If B is 3rd then A is not second OR
If A is 2nd then B is not 3rd
2. "A is not 2nd unless B is 3rd"
If A is 2nd then B is 3rd
If B is not 3rd then A is not 2nd
3. A comes before B unless E is before F
IF E is before F then A is after B
If A is before B then E is after F
4. A cannot be before B unless E is before F
If A is before B then E is before F
If E is after F then A is after B
Do i have these down correctly? Thanks.
- relevantfactor
- Posts: 118
- Joined: Fri Jun 22, 2012 1:13 pm
Re: Conditional statements that use "unless"
Unless is necessary even for games, so you cant flip the two, unless you use the contra-positive(in all statements). Also since unless will be the necessary, the sufficient would be negated. Just look at the examples.DSman wrote:For some reason I always have to stop and think about these types of conditional statements which just wastes time on LG so I want to write down a bunch and please correct me.
1. "A is 2nd unless B is 3rd" This would be:
~A2->b3
~B3->2A
2. "A is not 2nd unless B is 3rd"
A2->B3
~B3->~A2
3. A comes before B unless E is before F
~A>B-->E>F
~E>F-->A>B
4. A cannot be before B unless E is before F
A>B-->E>F
~E>F-->~A>B
Do i have these down correctly? Thanks.
And what you wrote seems to be correct, but I just skimmed

Does that help?
- Cerebro
- Posts: 235
- Joined: Thu Aug 09, 2012 9:22 pm
Re: Conditional statements that use "unless"
I see what you did there.relevantfactor wrote: Unless is necessary even for games, so you cant flip the two, unless you use the contra-positive(in all statements).
-
- Posts: 193
- Joined: Fri Dec 26, 2008 8:05 pm
Re: Conditional statements that use "unless"
The logic equivalent for unless is "if not" to indicate sufficiency.
Unless my shoes are tied, I will fall OR I will fall unless my shoes are tied
~ST -> F
Contrapositive
~F -> ST
Multiple ways to skin a cat
Unless my shoes are tied, I will fall OR I will fall unless my shoes are tied
~ST -> F
Contrapositive
~F -> ST
Multiple ways to skin a cat
- relevantfactor
- Posts: 118
- Joined: Fri Jun 22, 2012 1:13 pm
Re: Conditional statements that use "unless"
LolCerebro wrote:I see what you did there.relevantfactor wrote: Unless is necessary even for games, so you cant flip the two, unless you use the contra-positive(in all statements).

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- PDaddy
- Posts: 2063
- Joined: Sat Jan 16, 2010 4:40 am
Re: Conditional statements that use "unless"
Unless I am Handsome, I will be Unhappy.
H --> U
U --> H
- Lyov Myshkin
- Posts: 218
- Joined: Sat Jun 28, 2008 11:28 pm
Re: Conditional statements that use "unless"
always have a good example memorized rather than the formula since you could easily incorrectly remember a formula which doesn't already intuitively feel true to you, but it's pretty hard incorrectly reason what this 'unless' conditional must be (in terms of arrows and letters and such) from a good example.it doesn't rain unless there are clouds.
- DSman
- Posts: 1385
- Joined: Wed Jun 27, 2012 4:27 am
Re: Conditional statements that use "unless"
Thanks for the response but I'm confused about this one:relevantfactor wrote:Unless is necessary even for games, so you cant flip the two, unless you use the contra-positive(in all statements). Also since unless will be the necessary, the sufficient would be negated. Just look at the examples.DSman wrote:For some reason I always have to stop and think about these types of conditional statements which just wastes time on LG so I want to write down a bunch and please correct me.
1. "A is 2nd unless B is 3rd" This would be:
~A2->b3
~B3->2A
2. "A is not 2nd unless B is 3rd"
A2->B3
~B3->~A2
3. A comes before B unless E is before F
~A>B-->E>F
~E>F-->A>B
4. A cannot be before B unless E is before F
A>B-->E>F
~E>F-->~A>B
Do i have these down correctly? Thanks.
And what you wrote seems to be correct, but I just skimmed![]()
Does that help?
"A is 2nd unless B is 3rd" This would be:
~A2->b3
~B3->2A
Shouldn't this be
B3 -> ~A2
A2 -> ~B3
What you wrote and what I wrote both make sense to me. If B is 3rd, then A cannot be second. You wrote it a different way. you said that a is not second if B is third. Don't both of these make sense? Im confused.
- Ixiion
- Posts: 138
- Joined: Tue Aug 21, 2012 9:02 am
Re: Conditional statements that use "unless"
No, because you wroteDSman wrote:Thanks for the response but I'm confused about this one:
"A is 2nd unless B is 3rd" This would be:
~A2->b3
~B3->2A
Shouldn't this be
B3 -> ~A2
A2 -> ~B3
What you wrote and what I wrote both make sense to me. If B is 3rd, then A cannot be second. You wrote it a different way. you said that a is not second if B is third. Don't both of these make sense? Im confused.
B3 -> ~A2
Which means If B is 3rd, A is not 2nd. That's true, but that's also giving way to the possibility that A is not 2nd even if B is not 3rd. So, in your equation, you could mistakenly draw your diagram this way:
(B1) 2 3 (A4) and it would still follow that rule, but it would be incorrect.
A2 -> ~B3
Again, still correct, but even with BOTH of your rules here, none of them say that A MUST be 2nd, which is what the original rule said. So you could make a lot of mistakes this way.
The way relevantfactor wrote it:
~B3 -> A2
says that if B is not 3rd, A is 2nd. Which is more encompassing and says that A must be 2nd if B is not 3rd.
and ~A2 -> B3
if A is not 2nd, B must be 3rd, because otherwise A is always 2nd, and so there's only one time when A is not 2nd, and that is when B is third. That's better understood when you see ~B3 -> A2 first.
Does that make sense?
- banjo
- Posts: 1351
- Joined: Wed Nov 30, 2011 8:00 pm
Re: Conditional statements that use "unless"
This is the best way to think about it. No matter where it appears in a conditional sentence, unless = if..not. If you've taken any Latin, think of how you'd translate nisi.Joeshan520 wrote:The logic equivalent for unless is "if not" to indicate sufficiency.
-
- Posts: 34
- Joined: Wed Jul 20, 2011 10:21 pm
Re: Conditional statements that use "unless"
Just memorize "negate sufficient". Whatever you negate becomes sufficient.
- DSman
- Posts: 1385
- Joined: Wed Jun 27, 2012 4:27 am
Re: Conditional statements that use "unless"
Yep that clears it. Thanks for the help.Ixiion wrote:No, because you wroteDSman wrote:Thanks for the response but I'm confused about this one:
"A is 2nd unless B is 3rd" This would be:
~A2->b3
~B3->2A
Shouldn't this be
B3 -> ~A2
A2 -> ~B3
What you wrote and what I wrote both make sense to me. If B is 3rd, then A cannot be second. You wrote it a different way. you said that a is not second if B is third. Don't both of these make sense? Im confused.
B3 -> ~A2
Which means If B is 3rd, A is not 2nd. That's true, but that's also giving way to the possibility that A is not 2nd even if B is not 3rd. So, in your equation, you could mistakenly draw your diagram this way:
(B1) 2 3 (A4) and it would still follow that rule, but it would be incorrect.
A2 -> ~B3
Again, still correct, but even with BOTH of your rules here, none of them say that A MUST be 2nd, which is what the original rule said. So you could make a lot of mistakes this way.
The way relevantfactor wrote it:
~B3 -> A2
says that if B is not 3rd, A is 2nd. Which is more encompassing and says that A must be 2nd if B is not 3rd.
and ~A2 -> B3
if A is not 2nd, B must be 3rd, because otherwise A is always 2nd, and so there's only one time when A is not 2nd, and that is when B is third. That's better understood when you see ~B3 -> A2 first.
Does that make sense?
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