Er möchte auch sein altes Auto verkaufen, weil er nicht mehr fahren kann.

Möchte means would like to and is softer, more polite, and less forceful than will.

• Er möchte sein Auto verkaufen = He would like to sell his car
• Er will sein Auto verkaufen = He wants to sell his car

Grammatically, möchte is the usual modern form used like a polite version of mögen.

Because möchte works like a modal-style verb here.

In German, when you have a verb like möchte, the second verb usually goes to the end in the infinitive:

• Er möchte ... verkaufen

So the structure is:

• Er = subject
• möchte = conjugated verb in second position
• sein altes Auto = object
• verkaufen = infinitive at the end

This is very common in German:

• Ich kann Deutsch sprechen
• Sie will nach Hause gehen
• Er möchte sein Auto verkaufen

Sein means his.

Here, Auto is the thing being sold, so it is the direct object of verkaufen, which takes the accusative case.

Since Auto is a neuter noun (das Auto), the possessive word and adjective have to match that.

So:

• sein = his
• altes = old with the correct ending
• Auto = car

Together: sein altes Auto = his old car

Because Auto is neuter singular and it is preceded by the possessive sein.

After possessive words like mein, dein, sein, ihr, adjectives take what is often called mixed declension.

For neuter singular nominative/accusative, the adjective ending is -es:

• sein altes Auto
• mein neues Handy
• ihr kleines Kind

So altes is correct because:

• Auto is neuter
• it is singular
• it is accusative here
• it follows sein

Because weil introduces a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

So:

• weil er nicht mehr fahren kann

Compare:

• Main clause: Er kann nicht mehr fahren
• After weil: ..., weil er nicht mehr fahren kann

This is one of the most important German word order rules.

In a subordinate clause with a modal verb, the verb cluster goes at the end, and the infinitive usually comes before the conjugated modal:

• ..., weil er nicht mehr fahren kann

That is the normal order.

Compare:

• Main clause: Er kann nicht mehr fahren
• Subordinate clause: ..., weil er nicht mehr fahren kann

So the modal kann moves to the end because of weil.

Nicht mehr means no longer or not anymore.

So:

• er kann nicht mehr fahren = he can no longer drive

This expression is very common:

• Ich wohne nicht mehr in Berlin = I no longer live in Berlin
• Sie arbeitet nicht mehr hier = She doesn't work here anymore

It suggests that something used to be true before, but now it is not.

Auch means also or too.

In this sentence, it suggests that selling the car is an additional action or idea:

• Er möchte auch sein altes Auto verkaufen = He would also like to sell his old car

The exact focus of auch can depend on context, but here it most naturally means that this is one more thing he wants to do.

German word order with auch can be tricky, because its position can slightly change what is being emphasized. In this sentence, its placement is natural and common.

Because weil starts a new clause, and that clause needs its own subject.

So even though the subject is the same person, German still says:

• ..., weil er nicht mehr fahren kann

Just like in English:

• ..., because he can no longer drive

You cannot leave out er here.

Fahren often means to drive, but it can also mean to travel/go by vehicle.

Examples:

• Ich fahre nach Berlin = I’m going/traveling to Berlin
• Er fährt ein Auto = He drives a car

In this sentence, because we are talking about selling his car and not being able to fahren, the natural meaning is drive.

Because all nouns are capitalized in German.

So:

• Auto
• Mann
• Haus
• Zeit

This is a standard rule in German spelling and helps you spot nouns more easily.

It is in the accusative case.

That is because verkaufen takes a direct object — the thing being sold.

So in:

• Er möchte sein altes Auto verkaufen

the thing being sold is sein altes Auto, so it is accusative.

For this particular noun phrase, the form looks the same as nominative because Auto is neuter, but grammatically it is accusative.

Yes, but the word order would change.

With weil:

• Er möchte auch sein altes Auto verkaufen, weil er nicht mehr fahren kann.

With denn:

• Er möchte auch sein altes Auto verkaufen, denn er kann nicht mehr fahren.

The meaning is similar: because.

The difference is grammatical:

• weil introduces a subordinate clause, so the verb goes to the end
• denn is a coordinating conjunction, so normal main-clause word order stays the same

Both are correct, but weil is very common in everyday German.