Learn Hardcore German: Das Pflaster auf meinem Knie ist neu.

Pflaster (meaning a sticking plaster / band-aid) is neuter, so it takes the article das.
So the basic forms are:
- das Pflaster – the plaster / band-aid
- ein Pflaster – a plaster / band-aid

It’s not logical from meaning; it’s just a property of the word:

das Pflaster (neuter)
not der Pflaster (masculine)
not die Pflaster (feminine singular; die Pflaster can be plural, though — see next question).

What exactly does Pflaster mean? Is it always a band-aid?

Pflaster has a few common meanings:

Medical sticking plaster / band-aid
- This is the meaning in Das Pflaster auf meinem Knie ist neu.
- British English: plaster
- American English: Band-Aid / bandage
Pavement / cobblestones (as a kind of surface)
- das Pflaster can mean “paving” or “cobblestone surface”:
  - Das Pflaster der Straße ist alt. – The street’s paving is old.
Plural
- The plural of Pflaster is die Pflaster:
  - Ich brauche zwei Pflaster. – I need two plasters / band-aids.

So the exact meaning depends on context. With auf meinem Knie, it clearly means a band-aid.

Why is it auf meinem Knie and not auf mein Knie?

This is about case after the preposition auf.

The preposition auf can take dative or accusative:
- Dative = location (where something is)
- Accusative = direction / movement (where something is going to)

In your sentence it’s a location:

The plaster is on my knee (no movement).
So auf takes the dative case: auf meinem Knie.

If there were movement onto the knee, you’d use accusative:

Er klebt ein Pflaster auf mein Knie. – He sticks a plaster onto my knee.

So:

auf meinem Knie – dative (where it is)
auf mein Knie – accusative (where it is going)

What case is meinem Knie and how is it formed?

Meinem Knie is dative singular, neuter.

Breakdown:

The noun Knie:
- nominative: das Knie (the knee)
- dative: dem Knie (to/at/on the knee)
The possessive mein (my) declines like ein:
- nominative neuter: mein Knie
- dative neuter: meinem Knie

So:

auf + dative → auf meinem Knie
If you used the definite article instead of mein:
- auf dem Knie – on the knee

Why is it meinem Knie and not mein Knie or meine Knie?

Three things are happening at once:

Possessive adjective “mein”
- Base form: mein (my)
Neuter noun “Knie”
- Gender: neuter (das Knie)
Dative case (because of “auf” + location)
- Neuter dative ending for mein is -em → meinem

So:

mein Knie – nominative/accusative (e.g. Mein Knie tut weh – My knee hurts.)
meinem Knie – dative (e.g. auf meinem Knie – on my knee)

Meine Knie would be plural:

meine Knie – my knees (nominative/accusative)
auf meinen Knien – on my knees (dative plural, note the -n).

Why is it ist neu and not something like ist neues?

In ist neu, neu is a predicate adjective (adjective after a linking verb like to be).

In German, predicate adjectives do not take endings.
They stay in their base form, just like in English:
- Das Pflaster ist neu. – The plaster is new.
- Die Pflaster sind neu. – The plasters are new.
- Mein Knie ist neu. (weird, but grammatically) – My knee is new.

Compare this to an adjective before a noun, where endings are needed:

ein neues Pflaster – a new plaster
das neue Pflaster – the new plaster

So:

before a noun → adjective ending (neues, neue, neuer, etc.)
after sein/werden/bleiben → no ending (neu)

Could I also say Das Pflaster ist neu auf meinem Knie? Is the word order fixed?

You can say Das Pflaster ist neu auf meinem Knie, but it sounds unusual and slightly awkward in standard German.

Neutral, natural version:
- Das Pflaster auf meinem Knie ist neu.
Alternative with a different focus:
- Auf meinem Knie ist das Pflaster neu. (focus on on my knee)

In German, the middle field (between the verb parts) is fairly flexible, but not everything sounds equally natural.

Das Pflaster auf meinem Knie ist neu. – Most natural.
Das Pflaster ist neu auf meinem Knie. – Grammatically possible, but feels marked/odd.
- It might be used in very specific emphasis patterns, but it’s not the default.

What’s the difference between auf meinem Knie and an meinem Knie?

Both are possible, but they have different typical uses:

auf meinem Knie – on top of my knee (contact on the surface)
- Perfect for a band-aid stuck on the knee.
- Very literal: on the surface, like on the table → auf dem Tisch.
an meinem Knie – at my knee / on/around my knee (more general contact or location)
- Used more for:
  - Pain/injury at the knee: Ich habe Schmerzen an meinem Knie.
  - Clothing or things attached around it.

For a plaster stuck on the skin, auf meinem Knie is the most straightforward, physical “on-top” image.
An meinem Knie could be used, but it slightly shifts the feel to “at the area of my knee” rather than literally on the top surface.

How do you pronounce Pflaster and Knie?

Pflaster:

Pf: a combined sound, both p and f are actually pronounced.
Rough guide: PF-las-ter
- Pfl- like pf in Pfizer (in German) or a quick “p-f” sound.
- -a- like “u” in cup or “a” in flat, depending on accent.
- -ster like “stair” but with a German r at the end.

Knie:

In modern standard German, the k is usually silent.
It’s pronounced like “nie” in English (but with a long ee sound):
- Knie → roughly knee in English.

So the whole sentence sounds approximately like:

Das PF-las-ter auf mai-nem KNEE ist noi.
(with neu pronounced like English noy).

Why are Pflaster and Knie capitalized?

In German, all nouns are capitalized, no matter where they appear in the sentence.

das Pflaster – Pflaster is a noun → capitalized
mein Knie – Knie is a noun → capitalized

Adjectives, verbs, and most other words are not capitalized in the middle of a sentence:

neu (adjective) – lower case
ist (verb) – lower case

So the capitalization here is simply following the general rule: all nouns get a capital letter.

What’s the difference between Pflaster and Verband?

Both are used for things you put on injuries, but they’re not the same:

das Pflaster
- A small adhesive strip you stick over a cut or scratch.
- British: plaster; American: Band-Aid / adhesive bandage.
- Usually for minor wounds.
der Verband
- A bandage in the sense of gauze, wrapping, or larger dressing.
- Often wrapped around a limb or larger area.
- Used for more serious injuries, sprains, after surgery, etc.

So your sentence with Pflaster clearly refers to a small sticking plaster on the knee, not a big wrapped bandage.