#14 - Ethicist: The general principle—if one ought to do

[James Finch]

Hi Meercat,

This is a difficult question because the stimulus is trying to prove that a principle conditional statement can be false. So the initial principle being:

Ought to do something (O2D) Can do something (CD)

and the contrapositive:

CD O2D

The ethicist is arguing:

02D CD

by using a promise to meet as an example of something a person ought to do (02D) and the traffic jam making the person late as an example of making it impossible to fulfill the promise (CD). So the setup is just the same conditional argument made on principle. This seems like a solid argument, right? Well now we have to think about how negating the conditions work, ie the contrapositive. By using the negation of the necessary condition of the principle he's trying to argue against, must also show that the contrapositive isn't necessarily true, or:

CD O2D

Put into words, this would sound something like what answer choice (D) is describing: just because you can't do something doesn't mean you aren't still obligated to do it.

Using the Assumption Negation technique to test (D), we see that the contrapositive of the initial principle holds up, invalidating the ethicist's conclusion:

"The obligation created by a promise is relieved by the fact that the promise cannot be kept"

or:

CD O2D

Hope this clears things up!

[meercat44]

Thanks for this, James! I'm still stuck on one part - where you say the ethicist is arguing: 02D CD


Is it that the ethicist is saying, *sometimes* if you ought to do something, you can't do it?

[Malila Robinson]

Hi meercat44,
Yes, the ethicist is trying to argue that the principle may *sometimes* be false. So the example shows an instance where you ought to be doing something, but you can't do it.
Hope that helps,
-Malila

[chian9010]

The original principle = "Should do it -> can do it" (you should do it means you can do it)
The Ethicist argument = "Should do it -> not necessary can do it" (you should do it doesn't necessarily means you can do it)
Counterexample = You promise to meet a friend (which imply that you should do it). However, because of the traffic, you can't do it.

The original principle + promise = "promise to do it = should do it -> can do it" (If you promise to do it, then you should do it which means you can do it in order to full fill your obligation)
The Ethicist argument + promise = "promise to do it = should do it but doesn't mean you can do it to full fill your obligation


Negate D = Obligation created by a promise is relieved by the fact that the promise cannot be kept
If the negated D is true then no one would care if you can do it or can't do it because if you don't do it the obligation will be relieved.

Is it right? I think its hard to explain.

[Rachael Wilkenfeld]

Chian--

You got it!

The negation of answer choice (D) says that the obligation is relieved by impossibility. In that case, there would be no "ought to do" for the conditional. Therefore, the ethicist must be assuming the logical opposite. The obligation (the "ought") is not relieved by impossibility.

Great job.
Rachael

[natalierohrig]

I can’t understand why D is correct. I negated it and it strengthened the argument.

Logical opposite:
“The obligation created by a promise IS relieved by the fact that the cannot be kept.”

So, if not being able to keep the promise (traffic jam) relives your obligation (created by the promise), then the general principle - “if one ought to do something then one can do it” does not hold. Affirming the argument.

So I didn’t choose it.

Answer choice A fit my prephrase that “promise = ought.” So I chose A.

I’m not sure where I’m wrong on this one.

[Jeremy Press]

Hi Natalie,

I think you might've misunderstood the general principle (If one ought to do something, then one can do it) and how it relates to your correctly-understood negation of answer choice D.

The negation of answer choice D actually validates the general principle (thus hurting the argument). Think about the contrapositive of the general principle, which is: "if you can't do something, then you have no obligation to do it." That's the same as the negation of answer choice D, which is saying that if the promise can't be kept (i.e. you can't do the thing), the obligation to do it is relieved (i.e. you have no obligation to do it). Those are the same!

Does that help clarify the issue? I hope so!

Jeremy

[natalierohrig]

Jeremy,

After taking a second look back I see the correct way to reason about it now. Thanks for your explanation!

Natalie

[oscartheglopez]

Ok, I have read through the posts and this is the best way I can think of knowing why D is the correct answer.
The General principle is laid out as ought to do > can do
If I diagram out the example that the ethicist uses it would be
ought to meet friend > can't meet friend
So, even though in the example the person can't fulfill what they ought to do, that doesn't change the first half of the statement. I'm not sure how to figure this out with the contrapositive so I did it in this way but I'm not sure if I'm just basing things off the right answer or if this is a correct way to handle these questions in the future.

[Adam Tyson]

I think that's a fine way to go about it, oscartheglopez. The author is showing a case which they believe disproves the general principal, because it is a case in which the necessary condition does not occur. But for that to be useful in disproving the conditional principle, the author has to assume that the sufficient condition does occur! There's your prephrase - the author assumes that the person who promised to meet their friend still ought to do so even when they are unable to do so. No need to think about the contrapositive when you look at it this way!