Instead is an adverb. It means ‘as an alternative’.
- He didn’t buy a large loaf. Instead, he bought two small loaves.
- She didn’t go to Greece. Instead, she went to Italy.
- Don’t marry Peter. Marry me instead.
As an adverb instead goes at the beginning or at the end of a clause. When it goes at the beginning of a sentence, we usually separate it off with a comma.
Instead of is a preposition. Note that instead is not used alone as a preposition.
- I’ll have a piece of cake instead of cookies, please. (NOT I’ll have a piece of cake instead cookies.)
Here the phrase instead of is used as a preposition. Note that a preposition is always followed by a noun or a noun phrase which acts as its object.
- I don’t want cookies. Instead, I’ll have a piece of cake. Here the word instead is used as an adverb. An adverb doesn’t take an object.
- Can I have a laptop instead of a tablet computer?
- I would like to buy a house instead of a flat.
Instead of can be followed by an –ing form. Infinitives are not normally used.
- I spent the whole day in bed instead of going to work. (NOT I spent the whole day in bed instead of to go to work.)