Learn Hardcore German: Ich suche nach meinem Schlüssel im Haus.

Ich suche meinen Schlüssel. – literally “I search my key” = “I’m looking for my key.” (Accusative object)
Ich suche nach meinem Schlüssel. – “I (am) searching for my key.” (verb + preposition nach
- dative)

Using für (Ich suche für meinen Schlüssel) would sound wrong here, because für expresses “for the benefit of” or “intended for”, not the object of a search.

So is „nach“ required with suchen, or can I leave it out?

You can say it both with or without nach:

Ich suche meinen Schlüssel.
Ich suche nach meinem Schlüssel.

Both are correct and natural. Some speakers feel that suchen nach can sound a bit more like “investigate / search for something” (often for more abstract things: nach einer Lösung suchen – “look for a solution”), while suchen + Akkusativ is a bit more everyday/direct.

With concrete objects like a key, you will frequently hear both versions.

Why is it „meinem Schlüssel“ and not „meinen Schlüssel“?

Because nach always takes the dative case in German.

The noun is der Schlüssel (masculine).
Dative masculine for the possessive mein- is meinem.

A quick pattern for mein in the singular:

Nominative: mein Schlüssel (my key)
Accusative: meinen Schlüssel (I see my key)
Dative: meinem Schlüssel (I search for my key, after nach)
Genitive: meines Schlüssels (rare in everyday speech)

So nach + Dativ → nach meinem Schlüssel.

Could I say „Ich suche meinen Schlüssel im Haus.“ instead? Is that different?

Yes, that’s perfectly correct and very common:

Ich suche meinen Schlüssel im Haus. (no nach, so Akkusativ: meinen Schlüssel)
Ich suche nach meinem Schlüssel im Haus. (nach + Dativ: meinem Schlüssel)

In everyday conversation, „Ich suche meinen Schlüssel“ is probably more frequent than „Ich suche nach meinem Schlüssel“ when we talk about concrete objects. The meaning is basically the same; any nuance difference (slightly more “searchy” or “systematic”) is very subtle.

Why is it „im Haus“ and not „in dem Haus“?

„im“ is simply the contracted form of „in dem“.

in + dem Haus (dative, neuter) → im Haus

Both „in dem Haus“ and „im Haus“ are grammatically correct. In normal speech and writing, the short form „im“ is much more common.

Why is „Haus“ in the dative case here?

Because the preposition in can take dative or accusative, depending on meaning:

Dative = location (where? – wo?)
Accusative = direction/motion (to where? – wohin?)

In the sentence „Ich suche nach meinem Schlüssel im Haus.“ you are already inside the house and searching there, so it’s a location → dative:

in dem Haus / im Haus (dative, “in the house”)

If you were moving into the house, you’d use accusative:

Ich gehe ins Haus. = in das Haus (direction, “into the house”)

Why is it „im Haus“ and not „zu Hause“ if the meaning is “at home”?

im Haus literally means “in the building / in the house” – it describes a physical location inside a house.
zu Hause means “at home” (your home), and is more about the idea of home than the building itself.

So:

Ich suche nach meinem Schlüssel im Haus. – You are somewhere inside that house. It might be any house.
Ich suche zu Hause nach meinem Schlüssel. – You are at home (your place) looking for your key.

Both could refer to the same physical place, but im Haus sounds more like “inside the house/building”, zu Hause like “at home (as opposed to outside)”.

Why is the verb form „suche“ and not „suchen“ or „sucht“?

Ich is the 1st person singular (“I”). The present-tense conjugation of suchen is:

ich suche
du suchst
er/sie/es sucht
wir suchen
ihr sucht
sie/Sie suchen

So with ich, you must use suche.

Could the word order be „Im Haus suche ich nach meinem Schlüssel.“?

Yes, absolutely. German word order is flexible with these prepositional phrases. Some options:

Ich suche nach meinem Schlüssel im Haus. (neutral)
Im Haus suche ich nach meinem Schlüssel. (emphasis on “in the house”)
Nach meinem Schlüssel suche ich im Haus. (more emphasis on “my key”)

The main rule to respect is: in a statement, the conjugated verb must be in second position:

Im Haus (position 1) suche (position 2) ich nach meinem Schlüssel (rest).

How would I negate this sentence? Where does „nicht“ go?

You place nicht before the part you want to negate. Some options:

Negate the whole action:
- Ich suche nicht nach meinem Schlüssel im Haus.
  → “I’m not searching for my key in the house (at all).”
Say you’re not searching in the house (but maybe somewhere else):
- Ich suche nach meinem Schlüssel, aber nicht im Haus.
  → “I’m looking for my key, but not in the house.”
Say you’re not looking for the key (but for something else):
- Ich suche nicht nach meinem Schlüssel, sondern nach meinem Handy.

How do I pronounce „Ich suche nach meinem Schlüssel im Haus“?

Key points for an English speaker:

Ich: the ch is soft, like a hissy “h” made high in the mouth. Not like English “k” or “sh”.
suche: su- like “zoo”, -che again with the soft ch. Roughly “ZOO-he”.
nach: ch here is a bit harsher, in the back of the throat, like in German Bach.
meinem: ei sounds like English “eye” → “MY-nem”.
Schlüssel:
- Sch = “sh”
- ü is between “ee” and “oo” (round your lips as for “oo” but say “ee”)
- roughly [SHLYOO-sel]
im: short “i”, like English “im” in “improv”
Haus: au like “house” in English – very similar.

So very roughly: “Ish ZOO-he nahkh MY-nem SHLYOO-sel im Hous.”

What gender and plural does „Schlüssel“ have?

Gender: masculine – der Schlüssel (the key).
Plural: die Schlüssel (no change in the noun).

Examples:

Singular: Ich habe einen Schlüssel verloren. – I lost a key.
Plural: Ich suche nach meinen Schlüsseln. – I’m looking for my keys.

How would I say “I’m looking for my key in the house, but I can’t find it”?

A natural translation using the same structure:

Ich suche nach meinem Schlüssel im Haus, aber ich kann ihn nicht finden.

Notes:

ihn refers back to meinen Schlüssel (masculine, accusative).
finden = “to find”, so kann ihn nicht finden = “can’t find it.”