Critical Reasoning

When you're using the Negation Test on an ASSUMPTION question, you should negate only the speculative part of the conclusion: "Therefore, the breakup of the hull can be ruled out as the cause of the sinking."

Generally speaking, anything presented as a premise should be taken to be true, e.g. "The storm's violent waves would have caused separate pieces floating even briefly on the surface to drift apart."

Think of it like this:
CR argument:
Because of fact A, therefore claim C must be true.

We want to find the thing that's unstated that would link these two:
Because of fact A, (assuming condition B), therefore claim C must be true.

If we use the negation test, it would look like this:
Fact A is true. But if the opposite of condition B were true... claim C would not be true.
This would reveal that condition B (the assumption) was actually NECESSARY to the conclusion.

You don't want to say "if fact A weren't true..." because this changes the underlying logic structure of the entire argument.

Here's how we would apply the Negation Test to each answer choice:

Given:
- the hull was found in two pieces
- separate pieces on the surface would have drifted apart

If....

A. Ships as large as the Edmund Fitzgerald REGULARLY sink in non-violent weather.... does that suggest that the breakup of the hull CANNOT BE RULED OUT as the cause of the sinking?
Nope. Whether it happens regularly or not, it could be the hull... or not.

B. Under water currents at the time of the storm DID move the separated pieces of the hull together again..... does that suggest that the breakup of the hull CANNOT BE RULED OUT as the cause of the sinking?
Yes! If underwater currents can move the pieces back together, then it's possible that the hull split apart on the surface and the pieces drifted apart first.

C. Pieces of the hull WOULD NOT have sunk more quickly than the intact hull would have.... does that suggest that the breakup of the hull CANNOT BE RULED OUT as the cause of the sinking?
Not really. How fast or slow it sank doesn't seem relevant to where the pieces ended up.

D. The waves of the storm WERE violent enough to have caused the breakup.... does that suggest that the breakup of the hull CANNOT BE RULED OUT as the cause of the sinking?
This one is tough. There are times that framing the answers with negation is not 100% clear. In this case, I asked myself instead, "does it HAVE to be true that the waves were not violent enough to cause the breakup in order to conclude that the breakup of the hull did NOT cause the sinking?" Well, no. Just because the waves didn't break up the hull doesn't mean that the hull couldn't have broken up for some other reason.

This answer choice is a good example of the difference between ASSUMPTION and STRENGTHEN. This one might have been a right answer if the question had asked "which of the following strengthens the conclusion?" It adds a new premise that supports our conclusion. The distinction, though, is that it does not HAVE to be true in order for us to draw this conclusion from the given premises.

E. If the ship broke up before sinking , the pieces of the hull WOULD have remained on the surface for very long.... does that suggest that the breakup of the hull CANNOT BE RULED OUT as the cause of the sinking?
Nope. Again, this is a length of time issue. The argument is all about distance, so this doesn't matter.

Does that clarify things?