Or

Or is a conjunction that connects two or more possibilities or alternatives. It connects words, phrases and clauses which are the same grammatical type:

Which do you prefer? Leather or suede?

You can have some freshly baked scones or some chocolate cake or both.

We use or after the negative form of a verb, instead of and.

Compare

I like tea and coffee.	I like both tea and coffee.
I don’t like tea or coffee.	I don’t like tea and I don’t like coffee.

When we connect two or more nouns using or, we use a singular verb with singular nouns, and a plural verb with plural countable nouns:

A banjo or a mandolin is what we need. (singular nouns)

I think more pictures or ornaments are needed in this room. (plural nouns)

Either … or

For emphasis, we can use either … or:

You can pay either by cash or by credit card. (the same as: You can pay by cash or by credit card.)

Warning:

The negative form of either … or is neither … nor:

Neither Joe nor Maria will be at the wedding.

In more formal language we sometimes use nor instead of or, even when neither is not used. It sometimes comes after a pause when someone adds another option:

No one knew from where they came – nor to where they went.

Typical errors

We use or, not and, after the negative form of a verb:

There weren’t any facilities at all. There were no bathrooms, telephones or even pillows.

Not: There were no bathrooms, telephones and even pillows.

We only use or to connect alternative possibilities. We use and when we mean ‘in addition to’:

In this essay, I will discuss both the advantages and disadvantages of killing animals for food.

Not: I will discuss both the advantages or disadvantages …