Symbolic Logic and the LSAT
 North
 Posts: 4190
 Joined: Wed Mar 02, 2011 7:09 pm
Symbolic Logic and the LSAT
Hello you wonderful people.
Alright, almost entirely on the advice of this thread, I am currently taking a course in Symbolic Logic at my UG. I'm early in my LSAT prep, but I was wondering if anybody might have an idea where some of the more practical skills I'm picking up might come into play in LR and LG. In case Symbolic Logic doesn't mean the same thing everywhere, we're specifically studying Sentential (truth tables, derivations, SD and SD+ rules) and Predicate Logic (just started on this today by mapping out Predicate sentences).
Anyone who took the course find practical, midexam applications for it?
Alright, almost entirely on the advice of this thread, I am currently taking a course in Symbolic Logic at my UG. I'm early in my LSAT prep, but I was wondering if anybody might have an idea where some of the more practical skills I'm picking up might come into play in LR and LG. In case Symbolic Logic doesn't mean the same thing everywhere, we're specifically studying Sentential (truth tables, derivations, SD and SD+ rules) and Predicate Logic (just started on this today by mapping out Predicate sentences).
Anyone who took the course find practical, midexam applications for it?
 glucose101
 Posts: 423
 Joined: Sun Mar 29, 2009 12:23 am
Re: Symbolic Logic and the LSAT
I mean, you just have to know simple logic that I learned in middle school (contrapositives, negation, chains, etc)
 Jeffort
 Posts: 1899
 Joined: Wed Jun 18, 2008 4:43 pm
Re: Symbolic Logic and the LSAT
If you are taking a symbolic logic class just to study for the LSAT, you made a huge mistake. They don't teach you how to improve your score on the LSAT. If you try to apply stuff from the class to solving LSAT questions faster and more accurately you very well may damage how you score. If you want to take a class specifically to improve your LSAT score, there are several decent companies that offer focused "LSAT Preparation" courses that are pretty good for the task.
 Cosmo Kramer
 Posts: 141
 Joined: Fri Jun 05, 2009 12:11 am
Re: Symbolic Logic and the LSAT
I took the same class and thought it helped a lot. It may only be "simple logic," but it's unlikely you deal with it everyday and I felt like spending that amount of time looking for the logical chains made it second nature by the end of the semester. Will it replace studying actual LR questions? No. But you'll find that once you've gotten good at embedded proofs, the LR on the LSAT is a joke.
 cnyltiak
 Posts: 26
 Joined: Mon Jun 06, 2011 9:22 pm
Re: Symbolic Logic and the LSAT
I took a symbolic logic class and a critical thinking class, the latter of which covered some symbolic logic as well as more inductive types or logic. I took the critical thinking one first and I think it applied more directly to the LSAT as it discussed fallacies, validity, etc. The symbolic logic class helped with some stuff... For instance, doing translations of predicate logic (with those fancy 'some' or 'all' things) helped show the relationship between such statements and a lot of the translations we did remind me way too much of LSAT questions like 'all beautiful people are blah blah'. The symbols you use to negate, do conditions, and, etc. is also helpful in some LG and LR questions.
Really I don't think these two classes will have a huge impact on my LSAT score, BUT they definitely do help you see and understand the rationale behind the test and makes certain concepts easier to understand and learn. Plus they were pretty fun (except derivations with scope lines at first... Ugh) and easy A+s for me so I'm glad I took them!
Really I don't think these two classes will have a huge impact on my LSAT score, BUT they definitely do help you see and understand the rationale behind the test and makes certain concepts easier to understand and learn. Plus they were pretty fun (except derivations with scope lines at first... Ugh) and easy A+s for me so I'm glad I took them!
 Sloth Hero
 Posts: 233
 Joined: Sun Apr 17, 2011 2:32 pm
Re: Symbolic Logic and the LSAT
North wrote:Hello you wonderful people.
Alright, almost entirely on the advice of this thread, I am currently taking a course in Symbolic Logic at my UG. I'm early in my LSAT prep, but I was wondering if anybody might have an idea where some of the more practical skills I'm picking up might come into play in LR and LG. In case Symbolic Logic doesn't mean the same thing everywhere, we're specifically studying Sentential (truth tables, derivations, SD and SD+ rules) and Predicate Logic (just started on this today by mapping out Predicate sentences).
Anyone who took the course find practical, midexam applications for it?
Be careful with predicate, it can fuck you up. Logic as it is taught in Universities tends to have a higher burden of proof than the LSAT does.
Predicate logic does not allow you to reason from All to Some, but the LSAT does. (At least according to Powerscore).
...Damn Aristotle
Sentential logic is great, especially the translations. They should help you for the 'formal logic' LR questions.
Truth tables will not really help you that much. They don't help you derive anything, only what IS true.
And speaking of derivations, they won't help you that much. Maybe the simple 67 line conditional derivations will help you reason internally, but my class had some big and meaty 30+ line minimum derivations, and these won't help you at all really.
Sure they strengthen your abstract analytic ability, but I'm not sure how well this translates to LSAT performance... maybe it strengthens your neurons? I don't know, I'm not a scientist.
Anyways, I'm taking modal logic next spring (after I finish the LSAT lol). I'll post whether or not I believe this class would help, but it's mostly about proving the soundness and completeness theorem, so probably not.
But I deny that this class can "hurt you". Only that taking it solely for LSAT prep is a bad idea, because you'd be better off taking 'Intro to Derp' and using your extra time to study for the LSAT.
 albusdumbledore
 Posts: 1138
 Joined: Thu Nov 05, 2009 4:38 pm
Re: Symbolic Logic and the LSAT
Sloth Hero wrote:North wrote:Hello you wonderful people.
Alright, almost entirely on the advice of this thread, I am currently taking a course in Symbolic Logic at my UG. I'm early in my LSAT prep, but I was wondering if anybody might have an idea where some of the more practical skills I'm picking up might come into play in LR and LG. In case Symbolic Logic doesn't mean the same thing everywhere, we're specifically studying Sentential (truth tables, derivations, SD and SD+ rules) and Predicate Logic (just started on this today by mapping out Predicate sentences).
Anyone who took the course find practical, midexam applications for it?
Be careful with predicate, it can fuck you up. Logic as it is taught in Universities tends to have a higher burden of proof than the LSAT does.
Predicate logic does not allow you to reason from All to Some, but the LSAT does. (At least according to Powerscore).
...Damn Aristotle
Sentential logic is great, especially the translations. They should help you for the 'formal logic' LR questions.
Truth tables will not really help you that much. They don't help you derive anything, only what IS true.
And speaking of derivations, they won't help you that much. Maybe the simple 67 line conditional derivations will help you reason internally, but my class had some big and meaty 30+ line minimum derivations, and these won't help you at all really.
Sure they strengthen your abstract analytic ability, but I'm not sure how well this translates to LSAT performance... maybe it strengthens your neurons? I don't know, I'm not a scientist.
Anyways, I'm taking modal logic next spring (after I finish the LSAT lol). I'll post whether or not I believe this class would help, but it's mostly about proving the soundness and completeness theorem, so probably not.
But I deny that this class can "hurt you". Only that taking it solely for LSAT prep is a bad idea, because you'd be better off taking 'Intro to Derp' and using your extra time to study for the LSAT.
Explain what you mean by the bold. The LSAT doesn't use some version of logic that is somehow different from predicate logic. Logic is just logic.

 Posts: 287
 Joined: Mon Jun 06, 2011 6:08 pm
Re: Symbolic Logic and the LSAT
albusdumbledore wrote:Sloth Hero wrote:North wrote:Hello you wonderful people.
Alright, almost entirely on the advice of this thread, I am currently taking a course in Symbolic Logic at my UG. I'm early in my LSAT prep, but I was wondering if anybody might have an idea where some of the more practical skills I'm picking up might come into play in LR and LG. In case Symbolic Logic doesn't mean the same thing everywhere, we're specifically studying Sentential (truth tables, derivations, SD and SD+ rules) and Predicate Logic (just started on this today by mapping out Predicate sentences).
Anyone who took the course find practical, midexam applications for it?
Be careful with predicate, it can fuck you up. Logic as it is taught in Universities tends to have a higher burden of proof than the LSAT does.
Predicate logic does not allow you to reason from All to Some, but the LSAT does. (At least according to Powerscore).
...Damn Aristotle
...
But I deny that this class can "hurt you". Only that taking it solely for LSAT prep is a bad idea, because you'd be better off taking 'Intro to Derp' and using your extra time to study for the LSAT.
Explain what you mean by the bold. The LSAT doesn't use some version of logic that is somehow different from predicate logic. Logic is just logic.
False. There are a number of different forms of logic, all based on differing philosophical theories (propositional/truthfunction, predicate, etc.)

 Posts: 968
 Joined: Sat Feb 19, 2011 2:27 pm
Re: Symbolic Logic and the LSAT
glucose101 wrote:I mean, you just have to know simple logic that I learned in middle school (contrapositives, negation, chains, etc)
I mean, you don't really even need to know thiese or any "formal" logic terms. You just have to be able to think logically.
 albusdumbledore
 Posts: 1138
 Joined: Thu Nov 05, 2009 4:38 pm
Re: Symbolic Logic and the LSAT
TMC116 wrote:albusdumbledore wrote:Explain what you mean by the bold. The LSAT doesn't use some version of logic that is somehow different from predicate logic. Logic is just logic.
False. There are a number of different forms of logic, all based on differing philosophical theories (propositional/truthfunction, predicate, etc.)
You're missing my point. There are indeed many notations and forms of logic. But the underlying axioms that make logic even possible are always the same. They're the whole basis of reason. Things like the principle of noncontradiction, principle of identity, and law of the excluded middle. Whether it's a truth table or a syllogism, they follow the same rules at their roots. Which is why I was curious by what he meant by "Predicate logic does not allow you to reason from All to Some, but the LSAT does."
 Moomoo2u
 Posts: 349
 Joined: Mon May 17, 2010 3:38 am
Re: Symbolic Logic and the LSAT
My intro to logic course was very difficult and not very applicable to the LSAT.
The only thing that kind of helped was already knowing the truth tables and the meanings of: and, if not, or, if and only if, etc etc etc
if you are interested in the broader concepts and want some familiarity with the material then go for it, but as others have said don't think it will give you a significant boost on the LSAT or replace an LSAT prep course/studying on your own.
The only thing that kind of helped was already knowing the truth tables and the meanings of: and, if not, or, if and only if, etc etc etc
if you are interested in the broader concepts and want some familiarity with the material then go for it, but as others have said don't think it will give you a significant boost on the LSAT or replace an LSAT prep course/studying on your own.

 Posts: 111
 Joined: Wed Aug 12, 2009 5:26 pm
Re: Symbolic Logic and the LSAT
albusdumbledore wrote:There are indeed many notations and forms of logic. But the underlying axioms that make logic even possible are always the same. They're the whole basis of reason. Things like the principle of noncontradiction, principle of identity, and law of the excluded middle. Whether it's a truth table or a syllogism, they follow the same rules at their roots. Which is why I was curious by what he meant by "Predicate logic does not allow you to reason from All to Some, but the LSAT does."
Not that it matters much for the purposes of the post  in fact, it might help explain why taking a logic course can screw you up for the LSAT  but this isn't right. There are a large number of different systems of logic which differ substantially, not just in notation.
As Sloth Hero notes, in what has come to be called 'classical logic', 'For all x, Fx' doesn't entail 'For some x, Fx'. But, in Aristotelian logic, it does.
 Jeffort
 Posts: 1899
 Joined: Wed Jun 18, 2008 4:43 pm
Re: Symbolic Logic and the LSAT
Moomoo2u wrote:My intro to logic course was very difficult and not very applicable to the LSAT.
The only thing that kind of helped was already knowing the truth tables and the meanings of: and, if not, or, if and only if, etc etc etc
if you are interested in the broader concepts and want some familiarity with the material then go for it, but as others have said don't think it will give you a significant boost on the LSAT or replace an LSAT prep course/studying on your own.
+1
Most of the other comments in this thread are fine and dandy but have nothing of value to help squeeze out a few more LSAT points on test day. Continue with the logical talk though for everyone interested in it that is taking a rest from productive LSAT prep.
 albusdumbledore
 Posts: 1138
 Joined: Thu Nov 05, 2009 4:38 pm
Re: Symbolic Logic and the LSAT
tsutsik wrote:albusdumbledore wrote:There are indeed many notations and forms of logic. But the underlying axioms that make logic even possible are always the same. They're the whole basis of reason. Things like the principle of noncontradiction, principle of identity, and law of the excluded middle. Whether it's a truth table or a syllogism, they follow the same rules at their roots. Which is why I was curious by what he meant by "Predicate logic does not allow you to reason from All to Some, but the LSAT does."
Not that it matters much for the purposes of the post  in fact, it might help explain why taking a logic course can screw you up for the LSAT  but this isn't right. There are a large number of different systems of logic which differ substantially, not just in notation.
As Sloth Hero notes, in what has come to be called 'classical logic', 'For all x, Fx' doesn't entail 'For some x, Fx'. But, in Aristotelian logic, it does.
Right, but this isn't because the rules of logic are somehow different. It's because Aristotle doesn't distinguish between individual predications and universal predications the same way classical logic does. It's a difference in the interpretation of language (which I will grant, matters on the LSAT), not in "logic" itself (i.e. the basic axioms that make up a logical system). Either way, at this point it doesn't matter because I now understand his point, and he's right, knowing how the test makers want you to interpret that on the LSAT will matter.

 Posts: 287
 Joined: Mon Jun 06, 2011 6:08 pm
Re: Symbolic Logic and the LSAT
albusdumbledore wrote:TMC116 wrote:albusdumbledore wrote:Explain what you mean by the bold. The LSAT doesn't use some version of logic that is somehow different from predicate logic. Logic is just logic.
False. There are a number of different forms of logic, all based on differing philosophical theories (propositional/truthfunction, predicate, etc.)
You're missing my point. There are indeed many notations and forms of logic. But the underlying axioms that make logic even possible are always the same. They're the whole basis of reason. Things like the principle of noncontradiction, principle of identity, and law of the excluded middle. Whether it's a truth table or a syllogism, they follow the same rules at their roots. Which is why I was curious by what he meant by "Predicate logic does not allow you to reason from All to Some, but the LSAT does."
Again, false. See: Boolean v. Aristotelian (which some posters have alluded to as i'm writing this)
Though this is diverging from the LSAT, just simplifying it down to "they're the whole basis of reason" is like cramming physics, chemistry, and biology together as "the whole basis of scientific inquiry". While it is a true statement, it doesn't get us very far.
But, to the immediate point at issue, im sure that we can all agree that taking a logic course is only tangentially helpful. With only 1:30ish per question, you don't have time to dig into your stuff from the logic course, draw out a truth table, or symbolize the statements with predicate logic. It helps you think (more generally) about logic and flaws but doesn't play a key role in answering questions
Id rather just spend that time reading the LRB and LGB...

 Posts: 43
 Joined: Sun Dec 05, 2010 8:52 pm
Re: Symbolic Logic and the LSAT
Almost all classical logics allow the inference from a universal to the corresponding existential. The only way this wouldn't be allowed is if the existential operator is interpreted as having some sort of extra implications about existence that the universal lacks, and even then I think only models with empty domains would be problematic.
Also, the there are many logics that differ not just superficially. This is most common with modal logics, but even with nonmodal logics you have variances. For instance intuitionistic logics deny the inference from notnotp to p.
In any case I think all of this shows just how irrelevant the philosophical study of logic is to the lsat.
Also, the there are many logics that differ not just superficially. This is most common with modal logics, but even with nonmodal logics you have variances. For instance intuitionistic logics deny the inference from notnotp to p.
In any case I think all of this shows just how irrelevant the philosophical study of logic is to the lsat.
 Jeffort
 Posts: 1899
 Joined: Wed Jun 18, 2008 4:43 pm
Re: Symbolic Logic and the LSAT
I like the existential detectives in the movie I ♥ Huckabees. They really know their $hit.

 Posts: 16
 Joined: Sat Apr 30, 2011 12:38 am
Re: Symbolic Logic and the LSAT
I have to agree that formal logic courses as preparation for the LSAT are not helpful. We are dealing with the transitive property pretty much exclusively on the LSAT. A key problem the vast majority of test takers run into is a less than clear understanding of necessary and sufficient.
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