what is the meaning of "or"?

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hi45

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what is the meaning of "or"?

Postby hi45 » Sun Aug 21, 2016 9:09 pm

A or B --------> C

Does "or" mean A or B, but not both? If A and B come, does that mean C must come?

Thanks.

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USayinBoalt

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Re: what is the meaning of "or"?

Postby USayinBoalt » Sun Aug 21, 2016 9:13 pm

For the purposes of the LSAT "or" is usually inclusive unless it's explicitly stated that it can't be both or it's logically impossible for it to be both

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Deardevil

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Re: what is the meaning of "or"?

Postby Deardevil » Sun Aug 21, 2016 9:14 pm

If A = apples, B = blueberries, and C = cherries, A or B -> C means something like this:

If Anna likes apples or Bobby eats blueberries, then Candice prefers cherries.
If Anna likes apples, Candice prefers cherries.
Similarly, Bobby eating blueberries is sufficient to conclude Candice will prefer cherries.
What's more? If Anna loves them apples AND Bobby devours those blueberries, Candice still favors cherries. :mrgreen:

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Deardevil

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Re: what is the meaning of "or"?

Postby Deardevil » Sun Aug 21, 2016 9:18 pm

But watch out for "either-or" because that seems to be what is confusing you.

If a stimulus or scenario says "If Derek goes to prom, EITHER Erica will go OR Frederick will go, BUT NOT BOTH,"
then there can only be two people at the prom, assuming only these people are eligible. Won't be very fun, though; that's for sure.

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Sprout

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Re: what is the meaning of "or"?

Postby Sprout » Mon Aug 22, 2016 12:30 am

Deardevil wrote:But watch out for "either-or" because that seems to be what is confusing you.

If a stimulus or scenario says "If Derek goes to prom, EITHER Erica will go OR Frederick will go, BUT NOT BOTH,"
then there can only be two people at the prom, assuming only these people are eligible. Won't be very fun, though; that's for sure.

This. Otherwise on the LSAT, the or's are inclusive. Weird part of their logic games because it differs from actual formal logic in that way but yeah. Unless it states otherwise, the or's are inclusive.

Edit:
So to answer your question if either A or B come, then C too. If both A and B go, also C.

foggynotion

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Re: what is the meaning of "or"?

Postby foggynotion » Mon Aug 22, 2016 2:32 am

Sprout wrote:Weird part of their logic games because it differs from actual formal logic in that way but yeah. Unless it states otherwise, the or's are inclusive.


I'm surprised at this. When I studied formal logic in college, the inclusive "or" was always used. What variety of formal logic are you referring to? Just curious. Thanks.

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ek5dn

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Re: what is the meaning of "or"?

Postby ek5dn » Mon Aug 22, 2016 3:10 am

foggynotion wrote:
Sprout wrote:Weird part of their logic games because it differs from actual formal logic in that way but yeah. Unless it states otherwise, the or's are inclusive.


I'm surprised at this. When I studied formal logic in college, the inclusive "or" was always used. What variety of formal logic are you referring to? Just curious. Thanks.


+1 yeah, formal logic uses an inclusive "or" - I remember being confused by this as an undergrad b/c in common usage, "or" is exclusive

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Deardevil

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Re: what is the meaning of "or"?

Postby Deardevil » Mon Aug 22, 2016 10:58 am

"Or" should be inclusive unless we are talking IRL, which can go either way, and it makes sense.

If Gary were choosing which flavor of ice cream to get and came to the decision of vanilla OR chocolate,
yes, he is still pretty undecided, but he would not care too much which of the two flavors he ends up receiving.
Vanilla? Sweet. Chocolate? Awesome. And since either one works, clearly, both are fine, too. Unless you're afraid of gaining weight.

IRL, if Hannah were picking a pet, which will be a cat or dog, she probably means she is getting exclusively one.
But the idea still holds; she does not care which one she buys. If she did, she would've come down to one choice.

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Sprout

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Re: what is the meaning of "or"?

Postby Sprout » Mon Aug 22, 2016 12:42 pm

ek5dn wrote:
foggynotion wrote:
Sprout wrote:Weird part of their logic games because it differs from actual formal logic in that way but yeah. Unless it states otherwise, the or's are inclusive.


I'm surprised at this. When I studied formal logic in college, the inclusive "or" was always used. What variety of formal logic are you referring to? Just curious. Thanks.


+1 yeah, formal logic uses an inclusive "or" - I remember being confused by this as an undergrad b/c in common usage, "or" is exclusive

You guys are totally right oops my bad. Must've been thinking about the contrast with every day use not the contrast in actual logic. Sorry all and thanks for correcting me; I would be mortified if my shitty memory guided someone down a path to a crap LSAT score :oops:

ready2attend

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Re: what is the meaning of "or"?

Postby ready2attend » Mon Aug 22, 2016 9:57 pm

The standard for sentential logic is to treat OR as inclusive unless expressly stated otherwise

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scalawag

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Re: what is the meaning of "or"?

Postby scalawag » Mon Aug 22, 2016 10:32 pm

A or B --> C
A, B or both can be selected to trigger C.

A or B must be selected.

/A --> B
/B --> A

A or B must be selected but not both
A --> /B
B --> /A

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scalawag

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Re: what is the meaning of "or"?

Postby scalawag » Mon Aug 22, 2016 10:36 pm

If you select your sufficient your necessary always triggers.

If you select your necessary you are free to negate your sufficient condition.

If you look at the conditionals above with that in mind you will see why it is worded the way it is.



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