Struggling to Memorize Valid Args

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• JESUS LIVES 7 Core Member

  November 2017 26 karma

  Memorize if sufficient term is the same with the necessary terms being either (2 conditional relationships ->) or (2 most relationships) or (one conditional and one most) or (one conditional and one some) all create a some intersection for necessary terms .

  Memorize if sufficient term is the same but it is (2 some relationships) or a (Most and a some relationship) there is no necessary intersection.
• JESUS LIVES 7 Core Member

  November 2017 edited November 2017 26 karma

  Don't forget about contrapositives ! If you have 2 conditional relationships and the necessary terms are the same you can form contrapositives to get a some relationship between the contraposed necessary terms. I call this number ten on my list of valid arguments
  A>/B
  C>/B
  B>/A
  B>/C
  /Asome/C
• amedley88 Alum Member

  November 2017 378 karma

  Make some flash cards
• 1 Like

  TexAgAaron Alum Member

  November 2017 1723 karma

  @dfletch5 What in particular about them are you struggling with? Most Sagers would agree, it is more than just memorizing them, but understanding the relationship between the 2 items as well.

  Flashcards do help. I'd just also write down hypothetical premises w/ conclusion examples to go along with each valid argument form. That gives you another application tool that will further enhance your understanding of each argument form.

  Hope this helps.
• 2 Likes

  FerdaFresh Alum Member

  November 2017 edited November 2017 561 karma

  @akeegs92 said:
  @dfletch5 What in particular about them are you struggling with? Most Sagers would agree, it is more than just memorizing them, but understanding the relationship between the 2 items as well.

  This. "Memorizing" them by form isn't really the way to go... it's about understanding them. If you asked me to write out all the common valid and invalid argument forms in their ABC format I might draw a blank for a second, but I'd be able to identify if any of them were valid/invalid upon seeing them. That is the main goal of knowing them, because that is what you'll be doing when you write the LSAT.

  I'd probably be able to write them all out without missing any if given the time, but this practice would just be counter-intuitive. E.g. you should focus more on knowing why affirming the sufficient and denying the necessary are valid and why affirming the necessary and denying the sufficient are not.

  I don't know specifically what #7-9 were, but I vaguely remember that these deal with the "some" relationship between two variables (i.e. B and C) that are connected to a binding variable (i.e. A). A simple rule of thumb to remember these forms, if it doesn't come intuitively, is that all those with at least one conditional arrow connecting A to either B or C are valid. Otherwise, they are not valid (with the exception of two "most" arrows, which show that at least one of B and C will be part of a "some" relationship).
• 5 Likes

  LetsHigh5 Alum Member

  November 2017 703 karma

  Thanks to Matt Shinners (who scored a 180) from Manhattan Prep, I learned the following nifty strategy:

  1. List out the premises, correctly notating if it's an "all", "most", or "some" relationship for each one.
  2. Focus only on the sufficient side of the arrow (affirming the necessary is always invalid).
  3. See if 2 or more of the "strong" (all, most) elements on the sufficient side of the arrow can be linked up (NB: of course, you might have to take the contrapositive of at least one premise, though, especially on more difficult questions)

  After doing 1-3 above, you simply have to remember that:

  ALL + MOST = SOME, and it's valid.
  MOST + MOST = SOME, and it's valid.

  MOST + SOME or SOME + SOME is always invalid.
  No sufficient side linkage = no valid deductions to be made

  In fact, "some" will usually be the valid deduction, if there is one (NB: the one exception is "most A are B" and "all B are C", ergo "most A are C"). Therefore, when hunting for the correct answer on questions with quantifiers like this, check to see if the "some" answer choices are valid first, rather than simply going top-to-bottom.

  That's it! To summarize: list out the premises, try to link up the "strong" elements (all/most) on the SUFFICIENT side, and if you can, there is surely a "some" relationship to follow (with one exception, as stated above).

  When Matt told me this, it was amazing. It's soooooo much easier than trying to memorize all of the specific valid/invalid types. For me, the elegant simplicity of this method makes it more effective, especially when I'm in a time crunch and diagramming a tricky MBT, SA, or Principle question.