The argument from comparison is a first-order subject argument that supports a policy with another policy (1 sub PP).
ANALYSIS OF AN EXAMPLE
The president should not be replaced in war time, because one should not swap horses when crossing a stream
The arguer states in the conclusion that some action should not be carried out in a specific situation and supports this claim by stating that a similar action should not be carried out in a similar situation. Since the argument fits the form a is X, because b is X, it can be identified as a first-order subject argument. In this specific case, a is instantiated by ‘Replacing the president in war time’, X by ‘should not be done’, and b by ‘swapping horses when crossing a stream’.
Replacing the president in war time (a) should not be done (X), because swapping horses when crossing a stream (b) should not be done (X)
First-order subject arguments are further differentiated by identifying the types of statement in the conclusion and the premise. In this case, they are both statements of policy, which means that we are dealing with a first-order subject argument supporting a policy with another policy (1 pre PP).
The trivial name of first-order subject arguments is derived from the characterization of the relationship between the subjects a and b. In this example, the argument draws on the comparison between the policy mentioned in the conclusion, replacing the president in war time, and the policy mentioned in the premise, swapping horses when crossing a stream. We can therefore call such an argument an ‘argument by comparison’.