How to diagram Either/Or conditional statements

[lsat_novice]

Sometimes Either/Or conditional statements are diagrammed:

—A B (where the A is crossed out)

and sometimes they are diagrammed:

A B or C

What's the difference? And how do I know when it's appropriate to diagram one way over the other?

Thanks in advance!

[James Finch]

Hi LSAT Novice,

How the conditionals are diagrammed depends upon how they are given to us as written. For LSAT purposes, either/or can also include the possibility of both, unless that possibility is specifically excluded.
This blog post might help.
The first conditional you gave,
A B,
would correspond to a sentence meaning "At least one of A or B will be in the group."
The second example,
A B or C
corresponds to a sentence meaning "If A, then either B or C" (which includes the possibility of both; one must be present)

Do you have any specific examples that you find confusing?

[lsat_novice]

I was confused by this thread: viewtopic.php?t=7692

The first post in that thread diagrams the stimulus:

Person → Rich or Poor

Person → Honest or Dishonest

I had diagrammed the stimulus like lenawilhide (the last post on the first page): ~R --> P and ~H --> D

Thanks for including the link to that blog article. The article says:

In the following statements “either/or” does not necessarily mean “both,” and just means “at least one”:

1. Anne arrives before Bob or before Cathy.

2. Jack is either a better chess player than his mentor, or a better chess player than his opponent.

--So Anne could arrive before Bob AND before Cathy?
--And Jack could be better at chess than both his mentor AND his opponent?
--When I read those sentences it sounds like it should be one or the other, but I understand that for the purposes of the LSAT, "either/or" means "one or possibly both."

Thank you!

[lsat_novice]

I just encountered a problem (Preptest 11, Section 2, Question 3) that says Juanita must take either the number 12 bus or else the subway.

Does "Either...or ELSE" mean it's one or the other and can't be both?

[James Finch]

Hi LSAT Novice,

The "either...or else" construction would generally indicate a "one or the other, but not both" situation. More determinative, however, would be the commonsense inference that Juanita cannot be in two places at the same time and wouldn't be able to take two distinct forms of transportation to the same destination (unless both were required).

I should add that this shouldn't be too much of a cause for worry; LSAC strives to avoid these kinds of ambiguities and I can't think of a recent test (last 10+ years) where "either" has been an issue. Far more important is understanding the underlying conditional structure of the argument and how to quickly and efficiently diagram it.

Hope this helps!