Can "either" be used as an adverb, and if so does it require, allow, or prohibit the use of a comma when so used?

Question

Can either be used as an adverb, and if so, does it always take a comma when it is? And is the following statement correct in congruence with my question? I believe there is some mistake that I don't perceive:

He never talked to Sanena, and doesn’t like her either.

Another thing is that I feel this sentence of mine should have either without any comma, but somewhere in a sentence I have seen a comma placed right before the word either.

Could someone please clarify for me which particular conditions lead to using a comma before the word either?

Answer 1

Either can definitely be used as an adverb. It does not always have a comma with it. Your example sentence is grammatically correct:

He never talked to Sanena, and doesn't like her either.

The meaning of either is in addition. It is used in negative sentences to add emphasis.

Here is another example sentence using either as an adverb:

Many hotels in Bangkok are beautiful and not expensive either.

(notice: no comma)

Here are two example sentences that use either as an adverb and a there is a comma in each sentence:

The food in that restaurant is awful, and the tables aren't clean either.

I have never been there either, nor do I want to go.

Answer 2

Your sen­tence:

He never talked to Sanena, and does not like her either.

That comma is the least of your wor­ries with this par­tic­u­lar sen­tence. The real prob­lem is that and is a ter­ri­bly pol­y­se­mous con­junc­tion, one car­ry­ing too many pos­si­ble mean­ings for a sin­gle punc­tu­a­tion mark alone ever to dis­am­biguate com­pletely and safely.

First and fore­most, this and seems to join the two verb phrases never talked to Sa­nena with does not like her ei­ther. Sublim­i­nally, it also oc­cu­pies the gram­mat­i­cal role of the sub­ject and thus joins bother both sub­jects of the two re­spec­tive clauses.

Here’s a con­stituent tree of your sen­tence, cour­tesy of the CMU on­line link-parser tool:

(S (NP He)
   (VP (VP (ADVP never)
           talked
           (PP to
               (NP Sanena)))
       , and
       (VP does not
           (VP like
               (NP her)
               (ADVP either))))
   .)

Those sub­jects hap­pen to rep­re­sent the very same sub­ject here, but con­ceiv­ably might be an ad­di­tional sub­ject else­where:

• He went, and John fol­lowed.
• He went and was fol­lowed by John.

This im­plic­itly binds the ob­ject as well:

• He went, and John fol­lowed, to the des­ti­na­tion.

How­ever, this func­tion­al­ity is not used when the ob­ject is re­it­er­ated in the sec­ond clause.

More im­por­tantly, ei­ther can­not be used as a pred­ica­tive ad­verb in the sec­ond clause; that would in­stead need to be nei­ther as in

• .. and nei­ther likes her.

The pref­er­ence against that leads to the sus­pi­cion that ei­ther might be a sen­tence ad­verb:

• ...and ei­ther does not like her.

This ob­vi­ously sounds as if it should be fol­lowed by or:

• ...and ei­ther dis­likes her, or at least does not care.

This is se­man­ti­cally close to but ... any­way.

The real kicker is that ei­ther as a ter­mi­nal sen­tence ad­verb might also ap­ply to the first clause to con­fer a sym­met­ric re­la­tion. Ob­vi­ously Si­enna never talked to him, ei­ther. The corol­lary im­plied by anal­ogy is that Si­enna does not like him, al­though the per­spec­tive of the sen­tence does not al­low such in­fer­ence. Rather it im­plies the ques­tion for the fact. It would not be un­usual to fol­low up by stat­ing an asym­me­try:

• But Si­enna was se­cretly in love with him.

Another im­pli­ca­tion is that of how he could know not to like Si­enna. If ei­ther binds both clauses sym­met­ri­cally, he ei­ther does not yet like her be­cause he has not had the chance, or else he does not talk to her be­cause he does not like her. This state of mu­tual ex­clu­sion is the pri­mary func­tion of the ei­ther..or and nei­ther..nor dis­jun­tive con­struc­tions, which might be the rea­son that nei­ther too nor also has been used here.

As such, it makes sense to set off the sec­ond clause with a comma, as ad­po­si­tion, and to set off the ad­verb from the sec­ond clause. Other­wise ei­ther would serve no pur­pose at all be­cause leav­ing it out would re­tain the main con­junc­tive force rest­ing on the word and.