Common Flaws

Equivocation

Relying on uncertain terms.

ex) “The task is easy. Therefore, it is simple.” (easy=/=simple)

Exclusivity

Ignoring other possibilities

ex) “I’m not eating tacos, so I will eat spaghetti.” (could have something else)

Flawed Causation

Relying on mere correlation to prove causation

ex) “NBA players are more likely to be over 6ft, so being in the NBA must cause people to grow over 6ft”

Bad Analogy

Drawing an analogy without considering relevant differences

ex) “My dog Lulu needs insulin, so your dog Rick probably also needs insulin” (fails to consider Lulu has diabetes and Rick doesnt)

Incomplete judgment

Reaching a judgment without considering the relative pros and cons

ex) “Smoking helps you lose weight and manage appetite, so smoking is healthy” (not considering that it also causes cancer)

Part to whole

Claiming that what’s true of individuals belonging to a group is true of the entire group.

ex) “This break weights 1lb, so this brick wall must weigh 1lb” (not considering the whole may have a different quality)

Whole to part

Claiming that what’s true of an entire group must be true of individuals belonging to that group

ex) “This brick wall is 7ft high, so this brick must be 7ft high” (not considering the individual may have a different quality)

Logical force flaw

Relying on relatively weak premises to draw a relatively strong conclusion

ex) “I can ear a whole cheesecake in one sitting, so I will do it” (just because I can doesn’t mean I will)

Temporal

Claiming whats true of the past, present, or future must be true of other time periods.

ex) “Every time I’ve driven without a seatbelt, I haven’t gotten hurt. So today when I don’t wear my seatbelt, I won’t get hurt.” (not considering present may be different from the past)

Conditional fallacies

Making the sufficient condition for the necessary or vice versa

ex) “All dogs are fluffy, so this fluffy pet of yours must be a dog” (fluffieness is only necessary, not sufficient–fluffy pet could be a cat)

Sampling error

Relying on an unrepresentative sample to draw a conclusion about a group

ex) “A survey of 1,000 men found that most prefer ham to turkey. So most women prefer ham to turkey.” (maybe men and women differ)

Ad hominem

Attacking the person instead of their ideas

ex) “She stole my can opener last week, so her business proposal is clearly inferior to mine” (she may be a thief, but that doesn’t tell us about her business proposal)

Absence of evidence

Using a lack of evidence for an idea to conclude that the opposite is true

ex) “I’ve only met you over Zoom, so I have seen no evidence that you have legs. Therefore, you do not have legs.” (could still have legs even though haven’t seen evidence)

Perception vs. Reality

Using a belief or claim to conclude about reality

ex) “I believe that Santa Claus is real, so he exists” (maybe your belief is mistaken)

Percentage vs. Amount

Using a rate to conclude about a total amount, or vice versa

ex) “Last week 30% of my drinks were water, and this week 100% of them were water. Therefore, I drank more water this week than last week.” (what if last week 3 of your 10 drinks were water, but this week all you drank was a single glass of water)

Circular reasoning

Using a conclusion to prove itself

ex) “The constitution is authoritatuve because it says it is authoritative” (just restating the same thing twice)

Which five flaws are most common to see on the LSAT?

Equivocation, exclusivity, causal, incomplete comparison, incomplete judgment

What’s the general anticipation for a flaw on the LSAT?

Just because (premise) doesn’t mean (conclusion) because (reason/other possibility)