When can we omit the preposition "of" in such cases?

Question

I'm struggling to understand when we can omit the preposition "of" in cases when we use determiners in English (distributives and quantifiers).

I mean we all know that both "half the students were absent" and "half of the students were absent" are correct as well as "all my friends are there" and "all of my friends are there".

I would like to know the rule - when can we or can't we omit the "of"?

Scrolling through various examples online I've noticed that even with "all" and "half" it doesn't always apply and sometimes we can use it with other determiners and other times - not:

• Both of the cars were stolen. (can we omit "of"?)
• Half of every apple on the table was bitten. (can we omit "of"?)
• All of it was a lie. (can we omit "of"?)
• Several of my books were printed in Canada. (can we omit "of"?)
• Most of the people living in our town are teenagers. (can we omit "of"?)

Answer 1

All of the cars were stolen.

Both of the cars were stolen.

Half of the cars were stolen.

Several of the cars were stolen.

Some of the cars were stolen.

Few of the cars were stolen.

Most of the cars were stolen.

Many of the cars were stolen.

Or this:

All cars were stolen.

All the cars were stolen.

Both cars were stolen.

Both the cars were stolen.

Half cars were stolen.^no

Half the cars were stolen.^ok

Several the cars were stolen. ^no

Several cars were stolen.

Some the cars were stolen. ^no

Some cars where stolen.

Few the cars were stolen. ^no

Few cars were stolen.

Most the cars were stolen. ^no

Most cars were stolen.

Many the cars were stolen. ^no

Many cars were stolen.

{Several, some, few, most, many} do not accept another determiner. They must be used alone with the noun, or in a partitive construction with of.

Answer 2

There are no hard and fast rules which would apply in all situations. In English generally, many rules have exceptions, which often makes them practically useless as rules. Anyway, I can answer the rest of your question.

Both of the cars were stolen. (can we omit "of"?) Yes, you could say "Both the cars were stolen." or "Both cars were stolen"

Half of every apple on the table was bitten. (can we omit "of"?) Yes, but I'd say this is acceptable in colloquial English - but not everyone will agree, and according to some here it's rather controversial. Better to leave the "of" in there.

All of it was a lie. (can we omit "of"?) - No, but you could say "Everything was a lie." I suppose you could say "All was a lie" but it sounds a bit archaic/literary, although it might be OK in a poem. The "it" can't remain however.

Several of my books were printed in Canada. (can we omit "of"?) No, but you could say "Several books were printed in Canada", but then if you do that, you can't put "my" in there.

Most of the people living in our town are teenagers. (can we omit "of"?) No, but if you also omit "the", then you can say "Most people living in our town are teenagers"

Answer 3

The omission of "of" when used as in your question is slang, so it's unlikely to make much sense. I'm going to try to make up some rules anyway. Please tear them down; if they're too wrong I'll improve them.

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The meaning numbers below (e.g. 1.4) are referencing Wiktionary.

If the meaning is 1.3, 1.4, 2.1, 2.2, 2.3 (where it would change the meaning), 3.1 (where it might change the meaning), 3.2, 3.3 (where it might change the meaning), all of 4, all of 5 (especially 5.5, where its omission can cause any following indefinite article ("a" / "an") to mean "each" or "per"), all of 6, 7.2, 7.4, 8.2, 10.2 (you can't really... but it'd be interesting to see if the "exceptions" have a rule-like pattern)

Rule-like assertions:

If the meaning is 7.1, like in your question, you can omit "of" if:

• (colloquial) The word following "of" is an article and the word preceding "of" is an indefinite pronoun in this list:
  • both
  • all
  • half
  • there are probably more...
• The noun following the article is plural and you remove the article.

If the meaning is 8.1, 8.3 or 9.1, you can omit "of" if:

• You reverse the two noun phrases either side of "of" and it remains grammatically correct.

If the meaning is 10.1, you can omit "of" if:

• You convert the second noun to its adjectival form (e.g. "body" → "bodied," "leg" → "legged") and put a hyphen ("-") in between.

If the meaning is 10.3, you can omit "of" if:

• You remove the noun phrase preceding "of" (e.g. "at a speed of 40 m/s" → "at 40 m/s").
  CAVEATS:
  • This removes information.
  • This can be confused with 8.3 (e.g. "at the speed of sound").

You can always remove it without changing anything else if the meaning is:

• 7.3

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Conclusions:

• There are no complete rules about that can be described using English itself.
• English is horrible. What were we thinking?!

Answer 4

The general rule is actually simple. If you strike of, the noun in the prepositional phrase becomes the sentence noun and the old noun becomes an adjective. So the rule is when the original subject noun can convert to an adjective.