Why should we have of in this sentence?

Their products are of very high quality.

Can we simply drop the word of?

  • I wouldn't say we should add "of", but I'd say we can add "of". – J.R. Jan 15 '17 at 9:58
  • Amazing the number of things about English that I, as a native speaker, know, but don't know how I know! This is one, so I'm looking forward to someone explaining too. Incidentally, it's even OK to add an "a" and say, "Their products are of a very high quality". Clearly English is just having a laugh at humans' expense :-) – tkp Jan 16 '17 at 2:34
  • Then, may be we can say the food is of good taste, the rock is of rough surface, hong kong is of a nice place – Shahidan Shaari Jan 16 '17 at 7:10
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    Heh, @ShahidanShaari, I would say, don't go crazy :D. The "of" in your example sentence indicates that the products are "made of" or "come from" high quality materials. "Their products are [made] of very high quality [materials]." And so your other example sentences would be, "The good food is of [good] taste," "The rough surface is of the [rough] rock," and "The niceness of the place is of Hong Kong," but please note that these are very poetic uses of the language. Not as everyday as your example sentence. – Teacher KSHuang Jan 16 '17 at 12:17
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    @TeacherKSHuang this should be the answer :) – Andrew Jan 16 '17 at 21:26

The reason this is tricky is that "quality" is a noun, but that "high quality" is often used as an adjective phrase. When we say

The products are of high quality.

We are saying that high quality is something that the products have. This is probably the best option.

When we say:

The products are high quality.

We are saying that "high quality" is something the products are, similar to:

The products are red.

I'm not entirely sure that this is 100% proper grammar, but it's certainly very common in informal English. You can get away with it because "high quality" is recognized as an adjective.

Notice that you can't do this with every expression.

The products are dubious quality. Wrong

The products are of red. Wrong

The products are of dubious quality. Correct

This uses the same pattern, but the first phrase just sounds wrong because "dubious quality" is not idiomatic as an adjective the way "high quality" is. The second sentence is wrong because "red" truly an adjective is and not a noun in the way that "quality" is.


Their products are of very high quality

Their products are very high in quality

Their products are very high quality

Are all equally correct. The use of the extra words makes no difference to the meaning of the sentence.


This one's a little subtle and I probably can't provide a totally satisfactory answer

Their products are very high quality

isn't completely wrong. The meaning is unambiguous, but it sounds a little awkward, like an unfinished sentence. "high quality" by itself is an adjective in need of a noun. For example:

They have very high quality products.


They are very high quality machines.

To switch it around and avoid attaching "high quality" to the noun "products", and say "Their products are...", then the "of" is needed.

To make it more complicated, that use of "of" is not something you can universally apply. For example, the sentence

Their products are very good

is correct, but

Their products are of good materials

doesn't sound right. I think this is because using "of" makes it sound old fashioned (see below). Another more relevant example:

Their products are made with high quality materials

Here you see "high quality" attached to the noun "materials" again, avoiding the "of".

I should also mention that phrasing it with "of" makes the sentence sound formal, or old fashioned. It brings to mind a fancy person saying

"The bread at this bakery is of the very highest quality"

whereas an average person that wants to tell their friend that the bread is very good might say

"This bakery has some really good bread!"

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