• Apr 25th 2007, 06:30 PM
demon1
Which of these statements are believable??

a) "All of my 5-legged dogs can fly."
b) "I have no 5-legged dog that cannot fly."
c) "Some of my 5-legged dogs cannot fly."
d) "I have a 5-legged dog that cannot fly."

I think its (a) and (d), but im not sure. thanks.
• Apr 25th 2007, 06:48 PM
ThePerfectHacker
Quote:

Originally Posted by demon1
Which of these statements are believable??

a) "All of my 5-legged dogs can fly."

Let me do the first one.

It is saying "If there is a 5-legged man, than he flies."

THe conditional is always false.

Thus, the statement is always true.
• Apr 25th 2007, 08:06 PM
CaptainBlack
Quote:

Originally Posted by demon1
Which of these statements are believable??

a) "All of my 5-legged dogs can fly."
b) "I have no 5-legged dog that cannot fly."
c) "Some of my 5-legged dogs cannot fly."
d) "I have a 5-legged dog that cannot fly."

I think its (a) and (d), but im not sure. thanks.

a) As you cannot producea 5-legged dog which cannot fly as evidence
against it. Alternativly this claims that the null set is a subset of the null set.

b) Same as the first reason in a).

c) and d) are not beleivable unless you can produce a five legged dog. That
is they assert that the set of five legged dogs is non-null.

RonL