Self-study
Support Reptiles are air-breathing vertebrates with completely ossified skeletons; so Conclusion alligators must be air-breathing vertebrates with completely ossified skeletons.
Argument Summary
The stimulus starts with a general claim: reptiles are air-breathing vertebrates with completely ossified skeletons. From this premise, it concludes that alligators must therefore be air-breathing vertebrates with completely ossified skeletons.
Analysis of Argument Structure
Let's break down the structure of this argument. The premise is a definition, telling us that all reptiles fulfill certain criteria: being air-breathing vertebrates with ossified skeletons. Let's call all those characteristics together "X":
reptile → X
The second statement concludes that alligators must be X:
alligator → X
For this to be a valid conclusion, the argument must assume that all alligators are reptiles:
alligator → reptile
In other words, the structure we want will likely look something like this:
A → C (all A have some trait C)
Therefore, B → C
The key to the logic here will be the unstated assumption that B is a subgroup or subcategory of A: in other words, that all B are A (B → A).
13.
In terms of its logical █████████ ███ ████████ █████ ████ █████████ █████ ███ ██ ███ ██████████
a
Green plants take ██ ██████ ███████ ███ ███████ ██████ ████ ████ ███ ████ ██ ██ ███████ ████ █████ █████ ██ ██████ ███████ ███ ████████ ██████ ████ ███ ████
Correct. This follows the structure we saw in the stimulus: all A are C (all green plants take in carbon dioxide and release oxygen), therefore all B are C (all grass does the same thing). The assumption is that B is a subcategory of A: grass is a green plant.
b
Some red butterflies ███ █████████ ██ █████ ████ ████ ██ █████ ██ ████ ██████████ ███ █████████ ██ █████████ ██ █████ ████ ████ ██ ███
Incorrect. This follows a different structure than what we saw in the stimulus. This says that some A are C:
red butterfly ←s→ poisonous to birds
Then it concludes that one particular member of group A must be C: one particular red butterfly is poisonous to birds. But we don't know that this particular butterfly is part of the subgroup of red butterflies that are poisonous to birds. Remember that the assumption embedded in the stimulus was that some group B was a subgroup of A. In this case, we aren't dealing with the same kind of logic. We're going from a premise about one subgroup ("some") of a larger set A (red butterflies) to an unsupported conclusion about a specific member of A (one red butterfly).
c
Knowledge about the █████████ █████ ███ ██ ██████ ████ ██████ ██ ████████ █████████ ████ █ ████ ██ ███████ ███ ████ ███████ █████████ █████ ███ █████████ ██████
Incorrect. This is basically a sufficiency/necessity confusion. Just because books "can" provide knowledge of the empirical world doesn't mean any particular book must provide knowledge about the empirical world. This is a different structure than the stimulus follows.
d
Dierdre has seen █████ ████ ████████ ██ ██████ ██████ ███████████ ██ ███████ ████ ████ ████ ████ ████ ████ ███ █████ █ ████ ████████ ██ ███████████
Incorrect. This answer choice is tricky because it is structured similarly to the stimulus. All A are C (all films directed by Fassbender have been seen by Deirdre), therefore, one particular member of A must be C (a specific film by Fassbender has been seen by Deirdre). The problem is that we aren't dealing with another group, "B", that is assumed to be a subgroup of A. Instead, we're dealing with a specific item, this particular movie, which we are explicitly told is a member of A. So this is a different structure than the stimulus follows.
e
Skiers run a ████ ████ ██ ████ █████████ ██ ██ ██ ██████ ████ ████████ ███ ███ ████ ██ ████ █████ ███ ████ ██████ ███ ████████ █ ██████ ████ ██ ████ ██████
Incorrect. This is an argument about probability: because all members of a group have a high chance of something, one particular member of that group has likely experienced that thing at some point. This is a different structure from the stimulus, which relies on conditional logic and on the assumption that some group B is a subcategory of a larger group A, not on any predictions about an individual whom we are explicitly told is a member of A.