all, all of

all

In formal writing, omit the of after all. Remember the folk song:

All My Trials Not:

All of My Trials

all of

In two situations, however, you should include the of.

1. When the word following all is a pronoun.

all of them

But when that pronoun is possessive, omit the of:

She completed all her homework.

2. When the word following all is a possessive noun.

She read all of Grisham’s books.