🚀 go-pugleaf

seldin@alcor.concordia.ca ( JONATHAN SELDIN ) writes:

[stuff deleted]

>Think of A if and only if B.  This is A <--> B; A if B is clearly
>B --> A, and so A only if B must be A --> B.

>Another way to think of this is in terms of truth table values.
>In A only if B, the case that is excluded is that A is true and B
>is false; A only if B is true (truth functionally) in all other
>cases.  This gives us the truth table for A --> B.

I agree totaly in the mathemathical sense. But I think that when
we use the phrase "only if" in language, the "if" part is often
implicite. I would not say "Tom will come only if we invite him",
if I thought that even with an invitation, Tom might not come.
This "if" part might even be considered stronger in the phrase
"Only if we invite him, Tom will come to diner". So, I think
that if you're interpreting a text, the `A <-- B' part should
follow immediatly, while one should somehow look more closely
whether or not `A --> B' is implicitely assumend.

>Jonathan P. Seldin
>Department of Mathematics                 seldin@alcor.concordia.ca
>Concordia University			   seldin@vax2.concordia.ca
>7141 Sherbrooke Street West, Montreal, Quebec, Canada, H4B 1R6

Frank Teusink