## Sufficient--->Necessary with an "unless" clause

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JDSprintz

Posts: 12
Joined: Wed Jun 24, 2009 8:42 am

### Sufficient--->Necessary with an "unless" clause

Hi everyone,

Hope you are all having a good holiday weekend.

I have a quick question about logic games. One of the rules in the game I am working on is "R is not scheduled for Thursday unless L is scheduled for Monday". So, I took this to mean that if L is scheduled for Monday, then R is scheduled for Thursday. Apparently this is wrong. Can somebody explain why?

Thanks so much.

iwanta170

Posts: 445
Joined: Sat Apr 24, 2010 2:27 pm

### Re: Sufficient--->Necessary with an "unless" clause

It's because unless always signifies a necessary condition

Hence: If R is scheduled for Thursday, L is scheduled for Monday

005618502

Posts: 2577
Joined: Thu May 06, 2010 10:56 pm

### Re: Sufficient--->Necessary with an "unless" clause

Iwanta is correct. Unless refers to the result, then you negate the trigger. Pretty good strategy to use

feeblemiles

Posts: 111
Joined: Tue Oct 21, 2008 6:30 pm

### Re: Sufficient--->Necessary with an "unless" clause

R is not scheduled for Thursday unless L is scheduled for Monday.

If L is scheduled for Monday then R could be scheduled for Thursday.

R can only be scheduled for Thursday when L has been scheduled for Monday.

So if R is scheduled for Thursday, then L is scheduled for Monday.

Read unless statements as: if not (whatever came before "unless") then (whatever came after "unless")

So If not (R is not scheduled for Thursday) then (L is scheduled for Monday).

The not R is not scheduled for Thursday portion has two negatives, which cancel out to become R is scheduled for Thursday.

dakatz

Posts: 2422
Joined: Sat Mar 29, 2008 4:19 pm

### Re: Sufficient--->Necessary with an "unless" clause

JDSprintz wrote:Hi everyone,

Hope you are all having a good holiday weekend.

I have a quick question about logic games. One of the rules in the game I am working on is "R is not scheduled for Thursday unless L is scheduled for Monday". So, I took this to mean that if L is scheduled for Monday, then R is scheduled for Thursday. Apparently this is wrong. Can somebody explain why?

Thanks so much.

I always like to flip the phrase around to a positive form that seems to make sense more quickly to most people. So they tell you:

"R is not scheduled for Thursday unless L is scheduled for Monday"

I then say to myself, "so what if R IS scheduled for Thursday?" I flip around the first part of that phrase from "R is not" to "R is". The only way R could possibly be scheduled for Thursday is if L is on Monday. So you get:

If R Thursday ---> L Monday

JDSprintz

Posts: 12
Joined: Wed Jun 24, 2009 8:42 am

### Re: Sufficient--->Necessary with an "unless" clause

Ok, so "unless" always refers to the result.

If R is scheduled for Thursday, then L is scheduled for Monday. But L being scheduled for Monday doesn't by itself guarantee R being scheduled for Thursday.

Thanks so much!

dutchstriker

Posts: 276
Joined: Wed Aug 12, 2009 3:15 pm

### Re: Sufficient--->Necessary with an "unless" clause

http://www.top-law-schools.com/conditio ... oning.html

3/4 of the way down that page you'll find a section on "unless" conditional statements. There's also a worksheet if you need additional practice.

JDSprintz

Posts: 12
Joined: Wed Jun 24, 2009 8:42 am

### Re: Sufficient--->Necessary with an "unless" clause

HiLine

Posts: 210
Joined: Thu Dec 31, 2009 11:57 am

### Re: Sufficient--->Necessary with an "unless" clause

'A happens unless B happens' means that under 'normal' conditions, A will happen. If A does not happen, that is because of the 'effect' of B, so A not happening dictates that B happen. Thus the phrase can be rewritten as:
If A happens, B also happens
or simply:
Not A --> B

Edited: that also means either A happens or B happens or, at least one of A and B must happen, which is quite useful for Logic Games.

BrightLine

Posts: 259
Joined: Mon Mar 08, 2010 10:15 pm

### Re: Sufficient--->Necessary with an "unless" clause

I dont know why this has to be overly complicated.

"No X unless Y"

If X then there must be Y

AND

If there is no Y then there can be no X

Explanation: There can be no X unless there is Y. So if there is X then it follows that there must be Y.

confusedlawyer

Posts: 136
Joined: Thu May 27, 2010 11:21 am

### Re: Sufficient--->Necessary with an "unless" clause

No X unless Y
X= Omar goes to Vegas
Y= Shawn goes to vegas

Omar does not go to Vegas unless Shawn goes to Vegas

If Omar goes to vegas, Shawn goes to vegas
If shawn does not go to vegas, omar does not go to vegas
WRONG: If Shawn goes to Vegas, Omar goes to vegas
WRONG: If Omar does not go to vegas, Shawn does not go to vegas

Easy as Pie. MMmmm. Could go for a slice right about now