NA Questions

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  Logician Alum Member Sage ⭐

  October 2020 edited October 2020 2464 karma

  As I'm sure you've noticed, its really important to understand the difference between sufficient and necessary assumptions, so I'll try my best to explain!

  When we think of a sufficient assumption we're thinking of an assumption (unstated premise) that when added to the argument, makes it a valid argument. So what does this mean? Essentially all this means is that when the premise is added to the argument, it forces the conclusion to follow. Typically sufficient assumption answer choices tend to be stronger than necessary assumption answers, and rightly so as the task at hand is to force the conclusion to follow, where as most necessary assumption questions are merely helping the argument stand a chance (survive). So lets look at an example of a sufficient assumption.

  Premise: Tom is wearing a green shirt.
  Conclusion: Therefore, Tom will go to the park.

  Is this a good argument? of course not! how can someone reasonably conclude that just because Tom is wearing a green shirt he'll go to the park? So our job when attempting to make this argument valid is to add a premise, that when added to the argument, ensures that tom will go to the park. So here's a sufficient assumption.

  SA: Whenever Tom wears a green shirt, he goes to the park.

  When we add this assumption to the argument, its suddenly no longer a bad argument (structurally speaking), in fact its an iron-clad argument, in that its VALID.

  Premise 1: Whenever Tom wears a green shirt, he goes to the park.
  Premise 2: Tom is wearing a green shirt.
  Conclusion: Therefore, Tom will go to the park.

  Now contrast this with a necessary assumption. What does it mean for something to be necessary? well pretty much what the word means- its needed/required/essential for the argument to have a fighting chance. So naturally, this opens up the possibilities of more assumptions. here are a few:

  1) Tom will not die after he puts on his green shirt.
  2) Tom lives in a world that has a park.
  3) The world will not end before tom gets to the park.

  Imagine if these premises were negated, well then there would be no way in hell Tom could get his ass to the park, despite the fact that he's wearing his green shirt. Also, what's the consequence of adding one of these premises to the argument? lets see.

  Premise 1: Tom is wearing a green shirt.
  Premise 2: Tom lives in a world that has a park.
  Conclusion: Therefore, Tom will go to the park.

  Do you see how this is still a horrible argument? Adding the premise to the argument does almost nothing to the argument but make it POSSIBLE/CONCEIVABLE that Tom will go to the park, and in that sense, its NECESSARY for the argument.

  So if you apply this concept of necessity, you'll realize that a necessary assumption is also an assumption that MUST be true for the argument to hold, because if its not, the argument will fall apart.

  Now there are different "types" of necessary assumptions (see the cc for this), but at the core its really just semantics. The important thing is to really understand the distinction between something being sufficient vs necessary. Also keep in mind that there are instances where an assumption can be both necessary and sufficient at the same time.

  I hope this helps, good luck!
• cmoren21 Member

  October 2020 217 karma

  Thank you so much for this!! You did such a great job at explaining this. I'll definitely continue to work on NA using your explanation.
• 1 Like

  Logician Alum Member Sage ⭐

  October 2020 2464 karma

  No problem, happy it helped!