Environmentalist: When bacteria degrade household cleaning products, vapors that are toxic to humans are produced. U...

Alyona on February 3, 2020

Why not B?

Hi team, could you please explain why the correct answer is not B, I mean how would I check it using negation test? What is the logical opposite of this question? I clearly see (with my second guess) why A is correct, but I want to be able to exclude the wrong answers properly. Thank you.

3 Replies

Annie on February 3, 2020

Hi @Alyona1983,

(B) is incorrect because it states that toxic vapors are the only issue that may hurt humans when landfills are turned into parks. But, the argument does not require this to be the case as it only says that it is a thing which harms humans. To negate it, you would say that "converting a landfill into a public park could cause other damage to human health beyond just toxic vapors being produced." This would not hurt the argument, so the argument does not depend on this assumption.

Alyona on February 5, 2020

Thank you, Annie. Seems like I need to learn how to negate statements with "unless" in it more effectively.

Andrea on March 15 at 05:00PM

Hi @Alyona1983,

One quick way to remember how to diagram unless is to think "If not." Here's an example.

Let's imagine there's a criminal in a high security jail making plans for a great get-away.

Statement: The criminal will remain stuck in jail unless he digs a tunnel.

We thus know that IF the criminal does NOT dig a tunnel, he WILL remain stuck in jail. That's how "if not" works.

The contrapositive of that is if the criminal DOES remain stuck in jail, we know that he did NOT dig a tunnel.

However, here is the part you need to watch out for. What happens if the criminal DOES dig a tunnel? Does he get out of jail then?

The answer is that we don't know. Be careful with mistaken negations. All we can logically conclude from an unless statement is what happens when the exception (i.e. digging the tunnel in this case) does NOT occur (when it does not occur, we know the condition existing before the exception comes to pass i.e. remaining stuck in jail). The reason we don't know what happens when the exception DOES occur is because there could be more elements at play that affect the other condition. In this case, for instance, let's say the criminal DOES dig a tunnel. It would be incorrect to say then that he necessarily will NOT remain stuck in jail, because what if the police catch him making the tunnel and prevent him from getting out? Or, what if his tunnel only goes as far as the cell next door because he hits a concrete wall in the process? He could dig a tunnel, and still very well remain stuck in jail. We can't say for sure with the information in just that statement. If he digs a tunnel, that tunnel is the only possible exception that may lead to him not remaining stuck in jail. If he digs the tunnel, from there, he might get out of jail...but he also very likely might not.

Hope this helps you understand unless a little better!