Re: virus: SM

David McFadzean (
Mon, 29 Sep 1997 17:44:19 -0600

At 05:18 PM 9/29/97 -0500, Brett Lane Robertson wrote:
>Someone told me once that when you use words like "all" and "one" you need
>to be careful because they lend themselves to certain relationships that are
>not logical in the normal sense.

Try predicate calculus (first order logic).

"All humans have a common ancestor" can be translated to:

Ex.Ay human(y) & ancestor(x,y)

which means there exists an x such that for all humans,
x is an ancestor (appears in y's genetic lineage by definition).

x is the "common ancestor"

Actually, now that I look at it, x is our last (latest) common ancestor,
and all of her ancestors. But the statement, as written, says there is at
least one.

Not much can be validly inferred from this statement alone. Just paraphrases
with negations, disjunctions and implications thrown in such as:

Ex.~Ey human(y) -> ~ancestor(x,y)

translation: there is an x such that there isn't a human who doesn't have
x as an ancestor.

David McFadzean       
Memetic Engineer      
Church of Virus