Q17 - Every photograph, because it involves

[ManhattanPrepLSAT1]

joshmercer80 wrote:

Not sure which test this comes form, but it is an official LSAT problem:

[deleted copyrighted material]

I'm usually fairly proficient with logic reasoning questions, but I somehow got lost in the abstractness of the topic. Existentialism, ugh.

I'm glad you posted the question, but I deleted the copyrighted material.

Here's the core of this argument.

Evidence

Every photograph cannot express the whole truth, and in that sense, is false.

Conclusion

Nothing can be definitely proved with a photograph.

We're asked to find an assumption that would allow the conclusion to be properly drawn.

The gap in the reasoning is between not expressing the whole truth and definitely proving something. Answer choice (A) is the only answer choice that bridges the divide between the evidence and the conclusion.

(B) does not bridge to the conclusion regarding whether something can be definitely proven with a photograph.
(C) is about establishing the truthfulness of a photograph rather than definitely proving something with a photograph, subtle shift in language!
(D) is irrelevant. The distinction between corroborative evidence and additional evidence is not relevant.
(E) undermines the conclusion rather than supports it.

Clear things up?

[joshmercer80]

Yes, clears things up nicely. My problem was in pin pointing the supporting evidence. Once I had that, it was easy to see what their jump in logic was and what assumption would bridge that jump. Thank you.

[sumukh09]

Is this one diagrammed like this?

P ---> ~T [p = photograph, T = truth]

Conclusion:

P ---> ~DP [p = photograph, DP = definitely proved]


Gap: ~T --> ~DP or the contrapositive DP --> T

[lhermary]

Please go into more detail as to why C is wrong.


Thanks

[rinagoldfield]

(C) is tricky!

Let’s look back at the argument core:

Premise:

Photographs are true, but don’t depict the whole truth

-->

Photographs can’t definitively prove anything

Let’s think about an example. Let’s say Jenna has a photograph of her boyfriend kissing another girl. Does this photograph definitively prove that Jenna’s boyfriend is a cheater? Well, the photograph is "true" in the sense that it shows her boyfriend kissing someone who’s not Jenna. But it doesn’t depict the whole truth"”maybe the kiss is a scene in a play, or maybe Jenna’s boyfriend is kissing his sister. So the photograph, while "true" in a sense, doesn’t definitively prove cheating because it doesn’t depict the whole truth.

(C) says we don’t know ANYTHING about the truthfulness of the photograph. But we do know that the photo truly shows Jenna’s boyfriend kissing someone. Our question is whether that sliver of truth proves Jenna’s boyfriend to be a cheater or not.

In other words, (C) essentially undermines our first premise. That premise states that photographs are, in some senses, true. So we can determine the truthfulness of a photograph in some senses. The argument’s conclusion concerns what inferences we can draw that truth (did Jenna’s boyfriend cheat?).


Hope that helps.

[WaltGrace1983]

I felt like these answer choices were fairly vague, perhaps somewhat indicative of an older LSAT "style" than today. Here are my thoughts on the question (a tough one, I thought): This was a fairly easy to answer to get right but a really challenging one to prove why the incorrect answers are wrong!

Photographs cannot express the whole truth and thus photographs are false

-->

Nothing can ever be definitively proved with a photograph.

Notice how strong these words are: "nothing...can ever." The right answer better be a really ironclad one as soft language would presumably fail to definitely PROVE that the premise leads to the conclusion. The gap here is that, if something is false in one sense, does it mean that it can never prove ANYTHING? This analogy may not be completely synonymous but let's say we have a textbook. This textbook is from 1996 and it came out during a time when Pluto was a planet. This textbook provides hundreds and hundreds of pages of scientific data and a wealth of information. However, today we "know" that Pluto is not a planet. So in a sense this textbook if false because it doesn't provide the whole truth but does it mean that we can never definitively prove anything with this textbook? Not really.

(B) This doesn't support or reject the conclusion and it certainly doesn't completely bridge the gap between the premises and conclusion. This is really only tackling the premise that the photograph "cannot express the whole truth" but it never really mentions anything about the conclusion.

(D) This may actually weaken the argument. The conclusion says that we cannot ever definitely prove something with a photograph. Yet this answer choice says that "well maybe we can if we have other evidence while STILL using the photograph."

(E) This definitely weakens the argument. The conclusion says that we can NEVER EVER prove ANYTHING with a photograph. This says that, "well actually we can prove what is definitively true about that thing being photographed."

Now onto the tough one. (C) looks okay but the vagueness of the language is a little troubling. The problem with (C) is that it really only attacks the premise. The premise says that a photograph "cannot express the whole truth" while this AC just says that "determining the truthfulness" of the photo is not possible "in any sense." All this does is hurt the premise! That is not what we want! We want to bridge the gap between the premise and the conclusion.

(A) is an easy pick. It says that whatever is false in the sense that the argument uses cannot furnish proof. Well that is basically bridging the two sides of the argument word for word.