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

[JDSprintz]

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]

It's because unless always signifies a necessary condition

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

[005618502]

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

[feeblemiles]

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]

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]

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]

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]

Thanks for the link!

[HiLine]

Think about it this way:

'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]

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]

What helps me is think of an example in your head.

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