All refers to three or more items. It is used with plural nouns and pronouns.

I will take all three shirts.

I have invited all of them.

Before a noun with a determiner (e.g. articles, demonstratives and possessives), all and all of are both possible.

I have invited all my friends. OR I have invited all of my friends.

The cat has drunk all the milk. OR The cat has drunk all of the milk.

Before a noun with no determiner, we use all without of.

All children need love. (NOT All of children need love.)

All lights were out.

Before a pronoun, we use all of.

All of us can swim. (NOT All us can swim.)

Exercise

Complete the following sentences using all or all of. In some cases, both options are possible.

1. ……………………………….. my friends like riding.

a) all       b) all of                 c) either could be used here

2. She has invited ………………………………….. you.

a) all       b) all of                 c) either could be used here

3. ………………………………. children can be difficult.

a) all       b) all of                 c) either could be used here

4. She has eaten ………………………………….. the cake.

a) all       b) all of                 c) either could be used here

5. Give………………………………….. them my love.

a) all       b) all of                 c) either could be used here

Answers

1. All / all of my friends like riding.

2. She has invited all of you.

3. All children can be difficult.

4. She has eaten all / all of the cake.

5. Give all of them my love.