the plural of numbers combined with words

Question

Neun Stück Pizza isst man im Monat.

Why isn't it:

Neun Stücke Pizza isst man im Monat.

Another example is:

Ich habe gestern sechs Cognac getrunken.

which should be "Cognacs". What is its grammar? I'm B1+ and they never put this kind of stuff in books.

Answer 1

Neun Stücke Pizza essen man im Monat.

This would be wrong:

The subject in the sentence is "man", not "neun Stücke Pizza". And "man" is singular.

Neun Stück Pizza / Neun Stücke Pizza

The word "Stücke" is the plural of "Stück" which means: "piece".

However, the word "Stück" (but not "Stücke") can have another meaning in informal spoken language:

It is sometimes used to express the plural of something:

Was bieten Sie denn an?
Wir haben noch fünf Stück Pizza.
Gut. Dann kaufe ich zwei Stück.

What do you sell?
We have five pizzas left.
OK. Then I buy two of them.

Needless to say that in this case "Stück" is already plural and that no singular form exists.

Ich habe gestern sechs Cognac getrunken.

In German language you often see something like this when talking about liquids.

The words "glasses of" or "bottles of" are left out; the full sentence would be:

Ich habe gestern sechs Gläser Cognac getrunken.

Using the plural will change the meaning of the sentence:

1. Gestern habe ich drei Cognac getrunken.
2. Gestern habe ich drei Cognacs getrunken.

Means:

1. Yesterday I drank three glasses of Cognac.
2. Yesterday I drank three different types of Cognac.

Answer 2

The pattern for the first sentence is:

[number] + [unit] + [name for what is measured]

3 Meter Seide - 3 meters of silk
40 Liter Benzin - 40 liters of gasoline
7 Tonnen Schotter - 7 tons of crushed stone

6 Dutzend Eier - 6 dozen eggs
4 Millionen Euro - 4 million euros
2 Stück Zucker - 2 pieces of sugar

In the first 3 examples you have "real" physical units. The units in the last 3 examples are words for numbers, but they work the same way.

The examples Tonnen and Millionen show, that the unit normally is used in its plural form when the number is different from 1. The plurals of Meter, Liter and Dutzend are equal to the singular forms, so they don't help here.

But Stück is different. It behaves different when it is used as a "normal" noun or as a unit. When it is used as a unit, it's plural form is equal to its singular form. In other cases you have to add an -e:

• used as unit:

  1. Ich möchte bitte 2 Stück Zucker in meinen Kaffee.
  2. Wieviel Zucker möchtest du in deinen Kaffee? - Ich hätte bitte gerne 2 Stück.
  3. Wieviele Bücher sind in diesem Regal? - Ich schätze mal ca. 250 Stück.

• not a unit:

  4. Der Künstler hat innerhalb eines Monats drei neue Stücke komponiert.

The examples 2 and 3 also show, that the name for the things that are measured also can be omitted. It is enough tho know from the context what it is.

In example 4 the word "Stück" is not used as a unit. Here it is the name for the things that are counted. (Here: Stück = play or composition)

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The second example can be interpreted in two ways:

1. Sechs Glas Cognac
2. Sechs Cognacs

In 1 we have the same pattern as above. And "zwei Cognac" is just an ellipsis of this form. (Ellipsis = when something is omitted, that everybody would guess right.) But then Cognac behaves like water, milk, honey, air, ...: It is the name of an uncountable material, which means it can not be used in plural.

Two waters, 5 honeys and 7 airs really mean two kinds of water, 5 kinds of honey and seven kinds of air. And this is exactly the same in German. And so, in English and in German you can have two bottles of water (zwei Flaschen Wasser) but not two bottles of waters (zwei Flaschen Wässer). And this is also true for cognac.

In version 2, "a cognac" is not meant as the name of a liquid, but as a name of a portion of it, i.e. a glass of cognac. And when it is used this way, you can count it, and so you also have to use its plural form.

So, both versions are correct.