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  • Posts: 168
  • Joined: May 21, 2013
The answer key states that sentence three would be diagramed as such: H--> SF(crossed out)
Wouldn't the H have to be negated since its the sufficient condition in the sentence. I thought when we had sentences that had sufficient and necessary conditions in them that the condition with the necessary indicator word became the necessary condition and the remainder was negated and became the sufficient condition.

In this question the correct answer places the condition with the necessary indicator word as the necessary condition & places the remainder as the sufficient condition but doesn't negate the condition.

Does this rule only apply to these certain necessary conditions indicators: unless, until, except & without?
 Ron Gore
PowerScore Staff
  • PowerScore Staff
  • Posts: 220
  • Joined: May 15, 2013
Hi Sara,

Just to be clear, it appears you're referring to #4 on an earlier page, not page 234, of the weekend course book. (I think you likely have a more recent version of the coursebook, M9, than I have, M8, so the page numbers I have may be one off from yours. I show #4 on page 214.)

You're correct that the diagramming rule to which you allude, which we call the Unless Equation, only applies to special cases, in which the necessary condition is modified by unless, except, until or without. Otherwise, the only time negation typically comes into play in making a valid inference with a conditional relationship is when you reverse and negate both the necessary and sufficient conditions to get the contrapositive.

I think it's awesome, by the way, that you weren't fooled by the stimulus using the "only if" necessary condition indicator, which people often confuse with the sufficient condition indicator "if".

Please let me know if I can help you further.

  • Posts: 168
  • Joined: May 21, 2013
that makes sense. Thanks!

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