Obviously, I cannot both keep and break the same promise.

Mehran November 15, 2016

@r0hangupta the rule for "not both" is as follows:

(1) Pick a variable and make it the sufficient condition.

(2) Negate the other variable and make it the necessary condition.

You are negating a variable and making it your sufficient condition, which is incorrect (that is the rule for "either/or").

Our two variables here are KP and BP, so this would be diagrammed as follows:

KP ==> not BP
BP ==> not KP

Hope that helps! For a more in-depth review of these concepts, please review our video lesson on Sufficient & Necessary conditions.

TashaPenwell March 6, 2017

I can't see the answer. I have the same question as @r0hangupta. Thank you

Mehran March 13, 2017

@TashaPenwell which answer can you not see?

The answer explanation when reviewing the question or our explanation above on this message board?

olgamariecosme June 30, 2017

I have the same question and I can't see the explanation you've provided

halfhillbilly May 1, 2018

You show the "not" associated with the Y both times, while answer choice C shows "not" associated with X. Is this the issue? I also chose C.

Mehran May 2, 2018

Yes, (C) is diagrammed this rule as "either/or" as opposed to "not both."

Hope that helps! Please let us know if you have any other questions.

Raechel-Brodsky May 17, 2020

I still don't understand why it cannot be
not BP- KP? Mainly because aren't they b it h necessary conditions for each other?

Brett-Lindsay June 26, 2020

BP->KP would mean that if you break your promise, then you must keep your promise.

But we need if you keep your promise, then you cannot break it (KP -> XBP) or, if you break your promise, then you cannot keep it (BP -> XKP)

September 23, 2022

I don't understand how C is different from A