## Formal logic question...

Prepare for the LSAT or discuss it with others in this forum.
klikme

Posts: 2
Joined: Tue Aug 17, 2010 10:36 am

### Formal logic question...

I'm preparing lsat with Powerscore. Here I have a question regarding formal logic.

Some A's are B's.
No B's are C's.
All C's are D's.

Diagram : A some B <-/->(double not arrow) C -> D
Inferences : 1. A some not C
2. D some not B (according to the Bible)

Question : Isn't the inference "A some D" possible?
(For in the diagram "A some B <-/-> C" can be replaced with the inference 1 "A some not C", then this would make "A some not C -> D" and again "A some D".)

Thanks.

Nulli Secundus

Posts: 3175
Joined: Mon Jun 21, 2010 7:19 am

### Re: Formal logic question...

A some not C
C -----> D

Since the second part of first inference is "not C" and first part of second inference is "C" you cannot combine them. HTH.

d34d9823

Posts: 1879
Joined: Wed Apr 14, 2010 2:52 pm

### Re: Formal logic question...

nullisecundus wrote:A some not C
C -----> D

Since the second part of first inference is "not C" and first part of second inference is "C" you cannot combine them. HTH.

Yeah, some As being Bs doesn't preclude all As being Bs.

klikme

Posts: 2
Joined: Tue Aug 17, 2010 10:36 am

Thanks guys