Self-study
Support All known deposits of the mineral tanzanite are in Tanzania. ██████████ ███████ ██████ ████████ ████ █████████ ███████ ███ ██ ████████ ████ ██ ███████ █ █████ ███ ██████████ ████ █████████
The Argument Structure
This argument requires us to track three things: a mineral (tanzanite), a location (Tanzania), and a person (Ashley). All known tanzanite is found in Tanzania. Ashley collects only tanzanite. Therefore, Ashley is unlikely to collect a stone not from Tanzania.
Tanzania
all known tanzanite
Ashley
collects only tanzanite
Thus, Ashley is unlikely to collect a stone not from Tanzania
The reasoning pattern has three key features to match:
1. All known X is found in location Y (not "all X," just all known X)
2. Z interacts only with X
3. Therefore, Z is unlikely to interact with something outside Y (not "will never," just unlikely)
2. Z interacts only with X
3. Therefore, Z is unlikely to interact with something outside Y (not "will never," just unlikely)
The cautious language in the conclusion ("unlikely") matters. The stimulus says "all known deposits" (not all deposits) and concludes Ashley is "unlikely" to collect a non-Tanzanian stone (not that she never will). This is careful reasoning: since there could be undiscovered tanzanite elsewhere, the conclusion is probabilistic rather than absolute. The correct answer should match this caution.
What to Look For
We need an answer where all three parts line up: all known X is in Y, Z interacts only with X, and the conclusion says Z is unlikely (not certain) to interact with something outside Y.
26.
Which one of the following ██ ████ ███████ ██ ███ █████████ ██ ███ ████████ ██████
a
The lagoon on █████ ██████ ██ ████ ██ ████ ██████ █████ ███ ████ ██ █████ ██████ ███ ███████ ███ █████ ████ ███ ███████ ███ ████ ████ ████████ █████ ███ ████ █████ ████ ████ ███████ ███ ███████
The first premise says the lagoon is "home to many frogs," not that all known frogs on the island are in the lagoon. There could be plenty of frogs outside the lagoon too. Without establishing that all known frogs are in the lagoon, the argument doesn't match feature 1.
b
Every frog ever ████ ██ █████ ██████ █████ ██ ███ ███████ ███ █████ ██ ███ ██████ ███ █████ ████ ██ ███ ████ ██ ███ ███████ ███ █████ ███ ████ ███ █████ ███ ██ ██████ ████ █████ ███████ ███ ███████
"The frogs are eaten only by the owls" tells us that nothing else eats the frogs. But that's not the same as saying the owls eat nothing but frogs. Compare this to the stimulus: we're told Ashley collects only tanzanite, meaning tanzanite is the only thing she collects. (B) would need to say the owls eat only frogs, but instead it says frogs are eaten only by the owls. The "only" is attached to the wrong part. Since the owls might eat plenty of other animals besides frogs, including ones outside the lagoon, the conclusion doesn't follow.
c
Frogs are the ████ ███████ █████ ██ ████ ██ ███ ██████ ██ █████ ███████ ███ ████ ██ ███ ████ ██ █████ ██████ ████████ ██ ███████ ███ █████ ████ ███ ███████ ██████████ ███ ████ ███ ████████ ████ ██ ███ ██ ██████ ████ █████ ███████ ███ ███████
(C) is the trickiest wrong answer because it sounds like the stimulus, but the first premise points in the wrong direction. "Frogs are the only animals known to live in the lagoon" tells us what's inside the lagoon (just frogs, no other animals). But we need to know where the frogs are, not what else is in the lagoon. Compare: the stimulus says all known tanzanite is in Tanzania. It doesn't say tanzanite is the only mineral in Tanzania. Those are very different claims.
To see why this matters, think about what the first sentence of (C) allows. Maybe frogs live all over Scrag Island — on the beach, in the forest, in the lagoon. (C) tells us that frogs are the sole animal in the lagoon, not that the lagoon is the sole home of the frogs. So when the owls eat frogs from the island, those frogs could easily come from outside the lagoon. The conclusion that the owls are unlikely to eat something from outside the lagoon doesn't follow.
Stimulus
Tanzania
tanzanite
tanzanite
tanzanite
All known tanzanite is here.
Outside Tanzania: no known tanzanite
Tanzanite is confined to one place.
(C)
Scrag Island
Lagoon
🐸🐸
there are frogs here, no other animals
Beach
🐸❓
Forest
🐸❓
Frogs could be anywhere on the island!
Frogs are NOT confined to one place.
d
The only frogs ███ ██████████ ██ █████ ██████ ████ ██ ███ ███████ ███ ████ ██ ███ ███ ████ ██ █████ ██████ ████████ ████████ ██ █████ ██ ███ ███████ ██ ███ ████ ████ ████████ █████ ███ ██ ██████ ████ █████ ███████ ███ ███████
Every piece of (D) lines up with the stimulus.
Stimulus
All known tanzanite is in Tanzania.
Ashley collects only tanzanite.
Ashley is unlikely to collect a stone not from Tanzania.(D)
The only frogs discovered on the island live in the lagoon. ✓
Owls eat only frogs on the island. ✓
Owls will probably never eat an animal from outside the lagoon. ✓
The first premise confines (known) frogs to the lagoon, just like (known) tanzanite is confined to Tanzania. The second premise establishes that owls eat only frogs, just like Ashley collects only tanzanite. And the conclusion uses cautious language ("probably never") to say the owls are unlikely to eat something from outside the lagoon, just like Ashley is unlikely to collect a stone not from Tanzania.
e
Each frog on █████ ██████ █████ ██ ███ ███████ ██ ███ ██ █████ ██████ ██ █████ ██ ███ ████████ ███ █████ ██ ███ ███████ ██ ███████ ████ ██ ███ ██ █████ ██████ ████ ███ ████████ ████ █████ ███████ ███ ███████
(E) is close but too strong in two places. First, it states that "each frog on Scrag Island lives in the lagoon" as a definitive fact, not a claim about what's been discovered so far. Compare this to the stimulus's "all known deposits." Second, the conclusion says "no owl will eat anything that lives outside the lagoon," which is absolute rather than probabilistic. The stimulus carefully hedges with "unlikely." (E) drops the hedging entirely, making it a deductively certain argument rather than a probabilistic one.