Learn English – Either / Neither singular or plural

The use of words ending in "-ics" is governed by whether you are referring to a single body of knowledge or to objects/things.

But statistics has something more than this.

These statistics you presented are a pack of lies.

In the first sentence, "statistics" is used in the sense of "the field of statistics" or "the study of statistics". These are singular concepts. But in the second sentence, suddenly "statistics" is referring not to a single set of knowledge, but to multiple pieces of data. A plural verb should be used.

Until recently optics has only been three dimensional, and holography belongs to this form, too.

The optics in her telescope were superb.

Here again, "optics" is a field or concept. In the first sentence, the speaker is discussing optics in general, as a single whole. In the second, the speaker is talking about the particular lenses in the telescope.

For "mathematics", compare:

The field of mathematics is distinguished by its numerous contributors from across the world and through time.

The mathematics of quantum physics are hard for the average person to understand.

Generally speaking, if you are referring to a unified whole or a single thing, use the singular verb form. If you are talking about specific particular objects or subdivisions of a subject, use the plural form.

I think that 'either' here is being used in the sense that it is Joey, or 'me' (not both). So, the proper conjugation of the verb to have would be has.

You would generally use plural when you have 'either of', for example:

Would you tell me please whether either of us have to visit the manager tomorrow?