A sovereign or supreme ruler always rules in England. Here the disjunction is nominal; sovereign and supreme governor being different names for the same object. In all nominal disjunctives the inference is, that if an agent (or agents) do not perform a certain action under one name, he does (or they do) it under another.
Nominal disjunctives are called by Harris, subdisjunctives.
In the English language there is no separate word to distinguish the nominal from the real disjunctive. In Latin,
vel is considered by Harris to be disjunctive, sive subdisjunctive. As a periphrasis the combination in other words is subdisjunctive.
Both nominal and real disjunctives agree in this,—whatever may be the number of nouns which they connect, the construction of the verb is the same as if there were but one—Henry or John, or Thomas, walks (not walk); the sun, or solar luminary, shines (not shine). The disjunctive isolates the subject however much it may be placed in juxtaposition with other nouns.
[§ 620]. Either, neither.—Many disjunctives imply an alternative. If it be not this person (or thing) that performs a certain action (or exists in a certain state) it is some other. If a person (or thing) do not perform a certain action (or exist in a certain state), under one name, he (or it) does so under another. This alternative is expressed by the word either.
When the word either is connected immediately with the copula of a proposition, it is, if not a true conjunction, at least a part of a conjunctional periphrasis.—This either is or is not so.
When it belongs more to one of the terms of a proposition than to the copula, it is a pronoun,—Either I or you is in the wrong. It is either you or I.
I use the words, part of a conjunctional periphrasis, because the full conjunction is either + or (or neither + nor); the essential conjunctions being the latter words. To these, either (or neither) is superadded, indicating the manner in which the disjunction expressed by or (or nor) takes place; i. e., they show that it takes place in the manner of an alternative. Now, this superadded power is rather adverbial than conjunctional.
[§ 621]. From the pronominal character of the word either, when it forms part of a term, and from the power of the disjunctive, or, in isolating the subject of the verb, combined with an assumption which will be explained hereafter, we get at the principle of certain rules for doubtful constructions.