Learn Hardcore German: Ohne Isomatte würde mein Rücken am Morgen weh tun. - Without a sleeping mat my back would hurt in the morning.

ohne Isomatte sounds a bit more general and idiomatic, especially in spoken German, like:
- “without a sleeping mat / without any sleeping mat”
ohne eine Isomatte is a bit more explicit, focusing on one particular mat:
- “without a (single) sleeping mat”

German often drops the indefinite article after certain prepositions when speaking in general terms, especially with mit and ohne:

mit Auto fahren – to go by car
ohne Brille lesen – to read without glasses

So ohne Isomatte fits that common pattern.

What case is Isomatte in, and why?

Isomatte is in the accusative case.

The preposition ohne always takes the accusative:

ohne mich
ohne dich
ohne den Hund
ohne eine Isomatte

Here the full form would be ohne eine Isomatte → “without a sleeping mat”, and eine Isomatte is accusative singular feminine. Since nominative and accusative look the same for feminine -e nouns, the form Isomatte itself doesn’t change.

What exactly does würde … weh tun express? Is this a tense like future?

würde … weh tun is the Konjunktiv II (conditional) form, not a future tense.

It expresses a hypothetical or unreal situation:
- Ohne Isomatte würde mein Rücken am Morgen weh tun.
  = If I didn’t have a sleeping mat, my back would hurt in the morning.

English also uses a conditional here: “would hurt”.

So:

tut weh → real, factual: hurts
würde weh tun → hypothetical: would hurt

Could you also say Ohne Isomatte tut mein Rücken am Morgen weh? What’s the difference?

Yes, that sentence is grammatically correct, but the meaning changes:

Ohne Isomatte tut mein Rücken am Morgen weh.
→ Describes a real, regularly occurring situation. “When I don’t have a mat, my back (actually) hurts in the morning.”
Ohne Isomatte würde mein Rücken am Morgen weh tun.
→ Describes a hypothetical or imagined situation. “If I didn’t have a mat, my back would hurt (but maybe I usually do have one).”

So:

tut = real / habitual fact
würde … tun = imagined / conditional scenario

Why is tun at the end and in the infinitive?

That’s because würde is an auxiliary verb here, and the main verb appears in the infinitive at the end of the clause.

Structure:

würde (auxiliary) + weh tun (infinitive of the main verb)

German word order rule:
In a main clause with a modal or auxiliary verb, the finite (conjugated) verb goes in second position, and the main verb is an infinitive at the end:

Mein Rücken würde weh tun.
Ich würde kommen. – I would come.
Er möchte schlafen. – He would like to sleep.

So tun is at the end in infinitive form because würde is already conjugated.

Is weh tun one verb or two words? Why is weh separate from tun?

Functionally, weh tun / wehtun is treated as one verb meaning “to hurt”.

Base verb: wehtun
Typical finite form: tut weh
- Mein Rücken tut weh. – My back hurts.

Spelling:

In dictionaries, you’ll see wehtun written as one word.
In conjugated forms, tun is the verb and weh is placed after it:
- Mein Rücken tut weh.
With an auxiliary, you often see the infinitive written as wehtun:
- Mein Rücken würde wehtun.

Your sentence is using würde … weh tun. Many native speakers write it that way; others write würde … wehtun. Both are widely used; style guides generally prefer wehtun as one word in infinitive form.

What does am Morgen literally mean, and why not im Morgen?

am Morgen is a contraction of:

an + dem Morgen → am Morgen

Literally: “on the morning”, but idiomatically: “in the morning”.

We use an (dative) for certain time expressions in German:

am Morgen – in the morning
am Abend – in the evening
am Montag – on Monday

im Morgen (in + dem Morgen) is not used to mean “in the morning” in standard German; it sounds wrong in this context.

So am Morgen is simply the fixed, idiomatic way to talk about “the morning” as a time.

What’s the difference between am Morgen and morgens?

Both can translate to “in the morning”, but there’s a nuance:

am Morgen
- More like “on the morning / in the morning (of a particular day or occasion)”
- Slightly more specific or situational.
- Example: Morgen früh, am Morgen vor der Prüfung, bin ich nervös.
morgens
- Means “in the mornings / in the morning (as a habit, generally)”
- Stresses regularity or routine.
- Example: Morgens trinke ich Kaffee. – I drink coffee in the morning(s).

In your sentence, am Morgen suggests “in the (that) morning” after sleeping without a mat.
You could say:

Ohne Isomatte würde mein Rücken morgens weh tun.
That sounds more like “My back would hurt every morning (as a general habit) without a sleeping mat.”

Why does the sentence start with Ohne Isomatte? Could I start with Mein Rücken instead?

Yes, you can reorder it:

Ohne Isomatte würde mein Rücken am Morgen weh tun.
Mein Rücken würde am Morgen ohne Isomatte weh tun.

Both are grammatically correct. German allows flexible word order as long as the conjugated verb stays in the second position in a main clause.

Starting with Ohne Isomatte puts emphasis on the condition (“without a mat”), making it the topic frame of the sentence. Starting with Mein Rücken emphasizes the back instead.

In both cases, würde is still in the second position:

1st element: Ohne Isomatte → 2nd: würde
or 1st: Mein Rücken → 2nd: würde

Why is Rücken capitalized but weh is not?

In German:

All nouns are capitalized.
Adjectives and adverbs are normally not capitalized.

So:

Rücken – a noun (“back”) → capitalized.
weh – an adverb/adjective here (“sore / hurting”) → lower case.

Even though weh tun / wehtun works like one verb, only the verb part (tun) is a real verb, and weh stays an adverb, so it remains lower case.

Could I use a different verb instead of weh tun, like schmerzen?

Yes. Alternatives include:

schmerzen (a bit more formal or medical):
- Ohne Isomatte würde mein Rücken am Morgen schmerzen.
wehtun (your original verb):
- Ohne Isomatte würde mein Rücken am Morgen wehtun.

wehtun / weh tun is very common in everyday speech.
schmerzen sounds slightly more formal, bookish, or medical, but is perfectly correct.

How would you say this in the “would have hurt” (past unreal) form in German?

For a past unreal conditional, you use hätte + past participle:

Ohne Isomatte hätte mein Rücken am Morgen wehgetan.

Meaning:

“Without a sleeping mat, my back would have hurt in the morning.”

Structure:

hätte (Konjunktiv II of haben)
wehgetan (past participle of wehtun)

This contrasts with your original sentence:

würde weh tun → would hurt (now/in general, hypothetical)
hätte wehgetan → would have hurt (in the past, hypothetical)