The author uses the word "immediacy" (line 39) most likely in order to express
nicolebeton February 21, 2020
Contrapostives
(Sorry if this has posted twice, LSATMAX kept crashing)
I understand that we negate and reverse. However, the lecture states, "Lastly, if you are not in medical school, we can say you are not a doctor" (12:40-12:45 timestamp)
This reversed is: if you are a doctor, then we can conclude you went to med school.
When taking formal logic the (if, then) is very important in regards to antecedents and consequents.... Is this the same way the lesson is structured? It does not seem correct to state you are not currently IN medical school, therefore you are not a medical doctor. Maybe I was thrown off by the language used when you reversed the statement, making it currently in Med school, vs an inference that could have been made.
Also, Validity is important however, what about soundness and cogency when approaching the LSAT, are they important?
Is it better to not think of the formal/ symbolic logic I learned in my undergrad philosophy courses, and approach the LSAT's logical reasoning/ sufficient & necessary using LSATMAX's tips?
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Is this basically referring to modus ponens and modus tollens in formal logic?
shunheon February 21, 2020
Hi @nicolebet,
Thanks for the question! I think what the instructor meant to say was that the original statement
Doctor —> Medical School
Means that if you are a doctor, you went to medical school.
And so the contrapositive
~Medical School —> ~Doctor
Should mean that if you didn’t go to medical school (which I think the instructor meant by “if you aren’t in medical schoolâ€), then you aren’t a doctor. I would definitely say to feel free to use what you’ve learned in your formal/symbolic logic philosophy classes, though really the only logic that will really be tested on the LSAT is first-order logic. The types of questions being asked really aren’t that complicated if you’re a studier of logic (e.g. definitely no modal logic, and you don’t even really need to know predicate logic). Really the most complicated it gets isn’t significantly harder than having to apply De Morgan’s from time to time.
As for sound arguments, we always assume that the premises in the stimulus are true. Thus, if an argument on the LSAT presented is valid, we assume it is sound as well, though you won’t ever be asked about soundness. Same goes for cogency, you won’t be asked about it, but cogency I suppose is related to the idea of picking the “best†answer.
The part of the video you pointed out is just an application of modus tollens. Elsewhere, yes, you will use modus ponens, though you don’t have to actually know these terms. The LSATMAX terms are ways of making first-order logic accessible for people who aren’t familiar with logic.
Hope this helps! Feel free to ask any other questions that you might have.
