Logical ReasoningDifficulty: Hard

PT18 S2 Q9 Explanation

Nutritionist: Vitamins synthesized by chemists

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsNecessary Assumption

Keep going in LSAT Lab

  • Save & drill this skill build targeted practice sets from questions like this one

  • Video walkthroughs watch every question solved step by step

  • 81 official LSATs as questions, timed sections & full-length tests

Full official LSAT questions are available through LawHub. This page provides LSAT Lab's explanation, strategy, and review tools without republishing the full official question.

Stimulus

Nutritionist: Vitamins synthesized by chemists are exactly the same as vitamins that occur naturally in foods. Therefore, it is a waste of money to pay extra for brands of vitamin pills that are advertised more natural ingredients than other brands are.

What this question is testing

Necessary Assumption

Your task

Find the assumption the argument requires in order for its conclusion to hold.

Common trap

Answers that would help the argument but aren't strictly required (sufficient, not necessary).

Winning move

Negate each choice — the right one breaks the argument when negated.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
9.

The nutritionist’s advice is based on which one of the

Answer choices

  1. Too Strong5% picked this

    It is a waste of money for people to supplement their diets

    The author doesn't need to assume that "vitamin pills" in general are a waste of money. She's only saying that paying extra for certain vitamin pills is a waste of money; but she might still think it's a good use of money to buy the cheaper version.

  2. Too Strong: always15% picked this

    Brands of vitamin pills made of natural ingredients always cost more money than brands that

    Does the author need to assume that 100% of natural vitamin brands cost more than synthesized brands? Of course not. If we negate this, it will say "there is at least one brand of natural vitamins that costs the same or less than synthesized brands". That wouldn't weaken the author's argument. She'd say, "Cool. Feel free to buy that one if you want. Just don't waste your money on the natural-vitamin brands that are more expensive."

  3. Too Strong: All6% picked this

    All brands of vitamin pills contain some

    Would it hurt the author's argument if we said that "there is at least one brand of vitamins that is purely natural"? Not at all. She'd be like, "Cool, feel free to buy it if you want, unless it's more expensive, in which case you'd be wasting your money spending extra on it."

  4. Out of Scope: false advertising7% picked this

    Some producers of vitamin pills are guilty of

    This answer is very tempting. It's softly worded and it feels like an Inference we can pull out of the Premises (however, that's not our goal -- we're supposed to be thinking about Assumptions exist in the move from the the Evidence to the Conclusion). Would it hurt the author if we said, "No producers of vitamin pills are guilty of false advertising?" No, not really. First of all, her argument could be read as purely hypothetical -- she hasn't said anything that commits her to the idea that there actually ARE vitamin brands being advertised as "higher quality / more natural". I could make an argument that says, "You should NOT accept anyone's offer to give you a private ride to the moon" and it could be purely hypothetical. That argument doesn't assume that some people ARE offering private rides to the moon. Furthermore, while the author would say it's false to advertise that one vitamin pill contains higher-quality vitamins, she wouldn't say it's false to say that one vitamin pill has more natural ingredients. In a world where vitamin producers advertised their more expensive vitamins as having "more natural ingredients", our author could say, "They're not false advertising. It does have more natural ingredients. But there's no reason to pay extra money for natural ingredients since natural vitamins and synthesized vitamins are exactly the same."

  5. Correct68% picked this

    There is no nonvitamin ingredient in vitamin pills whose quality makes one brand worth more

    Why this is right

    If we negate this, we get "there is some nonvitamin ingredient in vitamin pills whose quality makes one brand worth more money than another brand." Does that weaken? For sure. That gives us a way to say that it wouldn't necessarily be a waste of money to buy a more expensive vitamin. Maybe the Vitamin C and Vitamin E in each of these pills is exactly the same, but one pill uses gelatin derived from animal stomachs to make their gummy vitamins whereas this other, more expensive pill uses a more humane nonvitamin ingredient to create its gummy. Or maybe they're both mango flavored, but one of them uses a nasty artificial mango flavor that gives the vitamin a weird aftertaste while the other one uses a delicious natural mango flavor that makes the vitamin more palatable.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free