Both either and neither are useful when you are talking about two options for something. Depending on whether you are talking about them in a positive way (good ways to lose weight, for example) or a negative way (things that you should not do if you want to lose weight), you can choose one or the other.
Either is positive. It means that you are talking about something in an affirmative light. If you have two options, for example, either one is good if both of them are good options. It can be used as a pronoun, conjunction, adjective, and adverb.
- Either one of the choices would put you in a good financial position, so you just need to choose the one that you like the most. (pronoun)
- People who help you by giving either home cooked meals or their professional expertise are those that really are great friends. (conjunction)
- You can pay in either currency; Hong Kong Dollars and Macau Pataca are both accepted here. (adjective)
- If you did not want it, then I definitely do not, either. (adverb)
Most of the time, either is paired with or. For example, either the blue dress or the red one will look great on you.
By contrast, neither is negative. It means that, when you use it, you will not have to add a “not” or a negative verb. If you use “not” or a negative verb with neither, you will create a lot of confusion. (Don’t do it!) Like either, neither can be use as a pronoun, conjunction, adjective, and adverb.
- Neither plan seems like a good idea, so I would caution you to really think about them before you carry them out. (adjective)
- Neither of our plans have worked perfectly, but it has just taught us to roll with the punches and adjust as necessary. (pronoun)
- I was expecting the company to contact me about their proposal, but they neither called nor emailed. (conjunction)
- If you do not leave the house today, neither will I. (adverb)
Notice that neither is paired with nor. Each of the sentences means that those things have not gone well (the second means that our plans have not worked perfectly, for example). The presence of the “n” on neither means that you do not have to add that the plans have not worked well.
Note also that when you are talking about yourself, you can agree by using either or neither. They have the same meaning in this case. You should say “me too” if someone tells you they are doing something that you will also do. If they tell you that they are not going to do something, you can respond “me either”. If you use neither, though, you will have to say “neither do I” or “neither will I”.
- I am planning on going to the party. Me too!
- I do not think I will make it to the party. Me either. The traffic is terrible.
- I do not think I will make it to the party tonight. Neither will I.