The argument from equality is a first-order subject argument that supports a policy with a fact (1 sub PF).
ANALYSIS OF AN EXAMPLE
Dutch royals should pay taxes, because every other citizen pays taxes
The arguer states in the conclusion that some people should do something and supports this claim by stating that other people are doing the same. 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 ‘Dutch royals’, X by ‘(should) pay(s) taxes’, and b by ‘every other citizen’.
Dutch royals (a) should pay taxes (X), because every other citizen (b) pays taxes (X)
First-order subject arguments are further differentiated by identifying the types of statement in the conclusion and the premise. In this case, the former is a statement of policy and the latter a statement of fact, which means that we are dealing with a first-order subject argument supporting a policy with a fact (1 pre PF).
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 idea that when it comes to paying taxes, Dutch royals should be treated equally to every other citizen. We can therefore call such an argument an ‘argument from equality’.