For several centuries there have been hairless dogs in western Mexico and in coastal Peru. It is very unlikely that a...

Daniel on February 17 at 05:13AM

Why not A?

Wouldn't a negation of A also make this argument fall apart? If the hairless dogs were found elsewhere in the world, then we can't say the dogs must have been traded between Mexico and Peru. Please explain, thanks!

4 Replies

on February 18 at 06:27PM

Hello @dannyod,

You may have a point that the negation of A does weaken the conclusion. However, weakening is not enough. We need the argument to fall apart completely. I'll explain why negating A does not do so.

Negation: Hairless dogs have been found in places other than western Mexico and coastal Peru.

Even if this is true, is it still possible that the dogs were brought to Mexico from Peru or vice versa. Maybe the dogs were introduced to other places centuries later. The argument can still stand.

Now let's try negating E.

Negation: Centuries ago, it was not easier to travel by boat between Mexico and Peru than by an overland route.

The author's conclusion is based on the idea that overland travel is extremely difficult, so it must have been by water. If we eliminate that premise, then the argument falls apart. The author has no reason to conclude that the dogs were bought by boat, when it was just as easy, if not easier, to bring them by land.

Daniel on February 24 at 01:17AM

Thanks for clarifying, but I am still confused. Isn't the author's conclusion that the dogs MUST have been traded from Mexico to Peru via boat. Answer A, in my view, degrades the conclusion because it no longer MUST be true (I.e. there is a legitimate alternative so no single explanation must be true). Sorry if this is nit picky, I'm just trying my best to understand. Why is the overwater v overland piece what we are paying attention to in this conclusion, vs the fact that it must have been traded between these two countries?

Daniel on March 21 at 08:24PM

Bumping up for clarification, thanks!

Daniel on April 8 at 03:12PM

@samA are you or another instructor able to clarify?